Combining the prayers
Content:
Combining the prayers according to the five school of thoughts
Combining the prayers when in a state of fear or journey or rain
Combining the prayers Without any excuse
Conclusion
 
Combining the prayers according to the five school of thoughts
It is confirmed that the prophet Muhammad (PBUH&HF) used to sometimes combine the prayers of Dhuhur and Asr (noon and afternoon), as well as the prayers of the Mughrib and I'isha' (sunset and night). These combinations were sometimes performed when the Muslims were in a state of fear or journey, war or when it was raining. At other times, they were performed without being in any of these states.

The prophet would sometimes delay the noon prayer and wait for the afternoon prayer (Ta'akheer): When it is time for the afternoon prayer, he would first pray the noon prayer (4 raka'ats) and after concluding it, he would pray the afternoon prayer. At other times, he would perform the noon payer at its time, and after concluding it, he would perform the afternoon prayer. This is referred to as Taqdeem. The same practice was applied to the mughrib and i'isha prayers. The companions followed this tradition as well.

The prophet combined the prayers when he was on a journey, such as Hujjat al-Wida'a and during the expedition of Tabuk. He also combined the prayers when he was in Medina and there was no state of fear, war, or rain. These narrations are acknowledged by the Sunnis sources as well as the Twelver Shia'a.

The following is a summary regarding the permissibility of combining the noon and afternoon prayers, as well as the sunset and night prayers, according to the five school of thoughts:

Imamis Hanbalis Shafi'is Malikis Hanafis
Permissible with an excuse or without one. Although, it is prefered to pray each prayer at its designated time. Permissible only if there is a genuine excuse such as travelling, rain, sickness, fear.

There are differences among the four Sunni school of thoughts with regard to the definition of travelling.

Permissible only if there is a genuine excuse such as travelling, rain, sickness, fear.

There are differences among the four Sunni school of thoughts with regard to the definition of travelling.

Permissible only if there is a genuine excuse such as travelling, rain, sickness, fear.

There are differences among the four Sunni school of thoughts with regard to the definition of travelling.

Permissible only at `Arafa and al-Muzdalifa, despite the existence of several authentic hadith that show this practice while travelling or under conditions of fear or rain.

Ibn Rush said in his book Bidayat al-Mujtahid:

وأما الجمع في الحضر لغير عذر، فإن مالكاً وأكثر الفقهاء لا يجيزونه، وأجاز ذلك جماعة من أهل الظاهر، وأشهب من أصحاب مالك

al-Tirmidhi said:

والعمل على هذا عند أهل العلم: أن لا يُجمع بين الصلاتين إلا في السفر أو بعرَفة. ورخَّص بعض أهل العلم من التابعين في الجمع بين الصلاتين للمريض، وبه يقول أحمد وإسحاق، وقال بعض أهل العلم: يُجمع بين الصلاتين في المطر، وبه يقول الشافعي وأحمد وإسحاق. ولم يرَ الشافعي للمريض أن يجمع بين الصلاتين

Combining the prayers when in a state of fear or journey or rain
The following narrations demonstrates the legality of combining the prayers, as practiced by the Imamis, Hanbalis, Malikis and Shafi'is when in a state of journey, fear or rain. These narrations are acknowledged as authentic by all these schools. The imamis however, rely on similar authentic narrations of the Imams of Ahlul Bayt.

Narrated 'Abdullah bin Yazid Al-Khatmi: That Abu Aiyub informed him that he offered the Maghrib and 'Isha' prayers together with the Prophet during Hajjat-ul-Wada.
Reference:
     Sahih Bukhari, Volume 5, Book 59, Number 698, Book: al-Maghaazi; Page 917, #4414 (Arabic version)

حدثنا عبد الله حدثني أبي حدثنا روح حدثنا مالك عن ابن شهاب عن سالم بن عبد الله عن أبيه
أن رسول الله صلى الله عليه وسلم صلى المغرب والعشاء بالمزدلفة جميعا
Reference:
     Musnad Ahmad ibn Hanbal, vol 5, p419 [entire book: page 1751, #23958];

Narrated Ibn 'Abbas: "The Prophet prayed eight Rakat for the Zuhr and 'Asr, and seven for the Maghrib and 'Isha prayers in Medina." Aiyub said, "Perhaps those were rainy nights." Anas said, "May be."
Reference:
     Sahih Bukhari, Volume 1, Book 10, Number 518, Book: Times of the Prayers; Page 128, #543 (Arabic version)

Narrated Salim's father: The Prophet used to offer the Maghrib and Isha' prayers together whenever he was in a hurry on a journey.
Narrated Ibn Abbas: Allah's Apostle used to offer the Zuhr and 'Asr prayers together on journeys, and also used to offer the Maghrib and 'Isha' prayers together.
Narrated Anas bin Malik: The Prophet used to offer the Maghrib and the 'Isha' prayers together on journeys.
Reference:
     Sahih Bukhari, Volume 2, Book 20, Number 209, Book: al-Maghaazi; Page 235, #1106, 1107, 1108 (Arabic version)
     Musnad Ahmad ibn Hanbal, vol 1, p217 [entire book: page 190, #1874];

You should note that the next three narrations from Sahih Muslim are under the title Combination of Prayers, When One is Resident. This indicates, that Muslim's understanding of this practice is not because of being under danger, fear, travelling or any special situation. But it is a general practice, with no specific excuse. Otherwise, why would the author (Muslim) place these narrations be under this title?

The proof for this argument is the existence of narrations that confirm that this practice was performed by the prophet and his companions under no excuse. These narrations are given in the next section.

Ibn 'Abbas reported that the Messenger of Allah (may peace be upon him) combined the prayers as he set on a journey in the expedition to Tabuk. He combined the noon prayer with the afternoon prayer and the sunset prayer with the 'Isha' prayer. Sa'id (one of the rawis) said to Ibn 'Abbas: What prompted him to do this? He said: He wanted that his Ummah should not be put to (unnecessary) hardship.
Reference:
     Sahih Muslim, Book 004, Number 1517, Book: al-Salat; Page 257, #(705)-51 (Arabic version)

Mu'adh reported: We set out with the Messenger of Allah (may peace be upon him) on the Tabuk expedition, and he observed the noon and afternoon prayers together and the sunset and 'Isha' prayers together.
Reference:
     Sahih Muslim, Book 004, Number 1518, Book: al-Salat; Page 257, #(705)-52 (Arabic version)

Mu'adh b. Jabal reported: The Messenger of Allah (may peace be upon him) combined in the expedition to Tabuk the noon prayer with the afternoon prayer and the sunset prayer with the 'Isha' prayer. He (one of the narrators) said: What prompted him to do that? He (Mu'adh) replied that he (the Holy Prophet) wanted that his Ummah should not be put to (unnecessary) hardship.
Reference:
     Sahih Muslim, Book 004, Number 1519, Book: al-Salat; Page 257, #(705)-53 (Arabic version)

حَدَّثَنَا قُتَيبَةُ أَخبرنَا اللَّيثُ بنُ سعدٍ عن يَزيدَ بنِ أَبي حَبيبٍ عن أَبي الطُفَيلِ عن مُعَاذِ بنِ جبلٍ: "أَنَّ النَّبيَّ صَلَّى الله عَلَيْهِ وَسَلَّمَ كَانَ في غزوةِ تَبُوكَ إِذَا ارتَحَلَ قَبلَ زَيغِ الشَّمسِ أَخَّرَ الظُّهرَ إِلى أَنْ يَجمَعَهَا إِلى العَصْرِ فَيُصَلِّيِهِمَا جميعاً وإِذَا ارتَحَلَ بَعدَ زَيغِ الشَّمسِ عَجَّلَ العَصْرَ إِلى الظُّهرِ وصَلَّى الظُّهرَ والعَصْرَ جميعاً ثُمَّ سارَ وكَانَ إِذَا ارتَحَلَ قَبلَ المغرِبِ أَخَّرَ المغرِبَ حتَّى يُصَلِّيَهَا مَعَ العِشاءَ وإِذَا ارتَحَلَ بَعدَ المغرِبِ عَجَّلَ العِشاءَ فَصَلاهَا مَعَ المغرِبِ". وفي البابِ عن عليٍّ وابنِ عُمَرَ وأَنسٍ وعَبدِ الله بن عَمْرٍو وعائشةَ وابنِ عبَّاسٍ وأُسَامةَ بن زَيدٍ وجابرٍ
Reference:
     Sunan al-Tirmidhi, vol. 2, #551 (أَبوابُ السَّفرِ 389 - بابُ ما جاءَ في الجَمْعِ بينَ الصَّلاتَينِ)
     Sunan al-Nisa'i, vol. 1 (كتاب المواقيت الوقت الذي يجمع فيه المسافر بين الظهر والعصر )
     Sunan Abu Dawud, vol. 1, #1206 to 1220 (كتاب الصلاة. تفريع أبواب صلاة السفر. -274- باب الجمع بين الصلاتين)
     Kanz al-U'ummal, by al-Muttaqi al-Hindi, vol. 12, #35398 (تتمة المعجزات ودلائل النبوة)
     Mu'ujam al-Tabarani al-Kabir, by Imam al-Tabarani (باب الميم. معاذ بن جبل الأنصاري. أبو الطفيل عامر بن واثلة عن معاذ)

More references:

  1. Musnad Ahmad ibn Hanbal:
    vol 1, p351 [entire book: page 288, #3288]
    vol 1, p360 [entire book: page 295, #3397]
    vol 5, p418 [entire book: page 1750, #23945]
    vol 5, p419 [entire book: page 1751, #23958]
    vol 5, p419 [entire book: page 1751, #23962]
Combining the prayers Without any excuse
The following narrations demonstrates that the prophet and his companions used to combine the prayers without being in a state of fear, in a state of journey, or danger, or rainfall.

Ibn 'Abbas reported: The Messenger of Allah (may peace be upon him) observed the noon and afternoon prayers together, and the sunset and Isha' prayers together without being in a state of fear or in a state of journey.
خبرنا قتيبة عن مالك عن أبي الزبير عن سعيد بن جبير عن ابن عباس -قال صلى رسول الله صلى الله عليه وسلم الظهر والعصر جميعا والمغرب والعشاء جميعا من غير خوف ولا سفر.
Reference:
     Sahih Muslim, Book 004, Number 1515, Book: al-Salat; Page 256, #(705)-49 (Arabic version)
     Sunan al-Nisa'i, vol. 1 (كتاب المواقيت. الجمع بين الصلاتين في الحصر)

Ibn 'Abbas reported: The Messenger of Allah (may peace be upon him) observed the noon and afternoon prayers together in Medina without being in a state of fear or in a state of journey. (Abu Zubair said: I asked Sa'id [one of the narrators] why he did that. He said: I asked Ibn 'Abbas as you have asked me, and he replied that he [the Holy Prophet] wanted that no one among his Ummah should be put to [unnecessary] hardship.
حدثنا عبد الله حدثني أبي حدثنا عبد الرزاق حدثنا سفيان عن أبي الزبير عن سعيد بن جبير عن ابن عباس قال:
جمع النبي صلى الله عليه وسلم بين الظهر والعصر بالمدينة في غير سفر ولا خوف قال: قلت: يا أبا العباس ولم فعل ذلك قال: ذلك أراد أن لا يحرج أحدا من أمته.‏
Reference:
     Sahih Muslim, Book 004, Number 1516, Book: al-Salat; Page 256, #(705)-50 (Arabic version)
     Sahih Muslim, Book 004, Number 1522, Book: al-Salat; Page 256, #(705)-56 (Arabic version)
     Musnad Ahmad ibn Hanbal, vol 1, p283 [entire book: page 238, #2557]
     Kanz al-U'ummal, by al-Muttaqi al-Hindi, vol. 8, #22778 ({الجمع)
     Mu'ujam al-Tabarani al-Kabeer, by Imam al-Tabarani ( باب الظاء - أحاديث عبد الله بن العباس بن عبد المطلب بن هاشم بن عبد مناف - أبو الشعثاء جابر بن زيد عن ابن عباس)

Ibn 'Abbas reported that the Messenger of Allah (may peace be upon him) combined the noon prayer with the afternoon prayer and the sunset prayer with the 'Isha' prayer in Medina without being in a state of danger or rainfall. And in the hadith transmitted by Waki' (the words are):" I said to Ibn 'Abbas: What prompted him to do that? He said: So that his (Prophet's) Ummah should not be put to (unnecessary) hardship." And in the hadith transmitted by Mu'awiya (the words are):" It was said to Ibn 'Abbas: What did he intend thereby? He said he wanted that his Ummah should not be put to unnecessary hardship."
‏و حدثنا ‏ ‏أبو بكر بن أبي شيبة ‏ ‏وأبو كريب ‏ ‏قالا حدثنا ‏ ‏أبو معاوية ‏ ‏ح ‏ ‏و حدثنا ‏ ‏أبو كريب ‏ ‏وأبو سعيد الأشج ‏ ‏واللفظ ‏ ‏لأبي كريب ‏ ‏قالا ‏ ‏حدثنا ‏ ‏وكيع ‏ ‏كلاهما ‏ ‏عن ‏ ‏الأعمش ‏ ‏عن ‏ ‏حبيب بن أبي ثابت ‏ ‏عن ‏ ‏سعيد بن جبير ‏ ‏عن ‏ ‏ابن عباس ‏ ‏قال
‏جمع رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏بين الظهر والعصر والمغرب والعشاء ‏ ‏بالمدينة ‏ ‏في غير خوف ولا مطر
‏في حديث ‏ ‏وكيع ‏ ‏قال قلت ‏ ‏لابن عباس ‏ ‏لم فعل ذلك قال كي لا ‏ ‏يحرج ‏ ‏أمته ‏ ‏وفي حديث ‏ ‏أبي معاوية ‏ ‏قيل ‏ ‏لابن عباس ‏ ‏ما أراد إلى ذلك قال أراد أن لا‏ ‏يحرج‏ ‏أمته
Reference:
     Sahih Muslim, Book 004, Number 1520, Book: al-Salat; Page 257, #(705)-54 (Arabic version)
     Musnad Ahmad ibn Hanbal, vol 1, p223 [entire book: page 194, #1953]
     Sunan al-Tirmidhi, vol 1, #187 (أَبوابُ الصَّلاَةِ. 138- بَابُ مَا جَاءَ في الجَمعِ بَينَ الصَّلاَتَينِ في الحَضرِ)
     Sunan al-Nisa'i, vol 1 (كتاب المواقيت. الجمع بين الصلاتين في الحصر)
     Sunan Abu Dawud, vol 1, #1211 (- كتاب الصلاة. تفريع أبواب صلاة السفر. 274- باب الجمع بين الصلاتين)
     Mu'ujam al-Tabarani al-Kabeer, by Imam al-Tabarani ( باب الظاء. أحاديث عبد الله بن العباس بن عبد المطلب بن هاشم بن عبد مناف. أبو الشعثاء جابر بن زيد عن ابن عباس.)

حدثنا عبد الله حدثني أبي حدثنا يحيى عن داود بن قيس قال: حدثني صالح مولى التوأمة عن ابن عباس قال:
جمع رسول الله صلى الله عليه وسلم بين الظهر والعصر والمغرب والعشاء في غير مطر ولا سفر قالوا: يا أبا العباس ما أراد بذلك قال: التوسع على أمته
Reference:
     Musnad Ahmad ibn Hanbal, vol 1, p346 [entire book: page 284, #3235];

حدثنا عبد الله حدثني أبي حدثنا سفيان عن أبي الزبير عن سعيد بن جبير عن ابن عباس قال:
صليت مع رسول الله صلى الله عليه وسلم ثمانيا جميعا وسبعا جميعا قلت لابن عباس: لم فعل ذاك قال: أراد أن لا يحرج أمته
Reference:
     Musnad Ahmad ibn Hanbal, vol 1, p349 [entire book: page 286, #3265];

عن ابن عباس قال
صليت مع النبي صلى الله عليه وسلم ثمانيا جميعا، وسبعا جميعا بالمدينة
Reference:
     Kanz al-U'ummal, by al-Muttaqi al-Hindi, vol. 8, #22774 (الجمع)

Ibn 'Abbas reported: I observed with the Apostle of Allah (may peace be upon him) eight (rak'ahs) in combination, and seven rak'ahs in combination. I (one of the narrators) said: O Abd Sha'tha', I think that he (the Holy Prophet) had delayed the noon prayer and hastened the afternoon prayer, and he delayed the sunset prayer and hastened the 'Isha' prayer. He said: I also think so.
وحدثنا أبو بكر بن أبي شيبة. حدثنا سفيان بن عيينة عن عمرو، عن جابر بن زيد، عن ابن عباس قال:
صليت مع النبي صلى الله عليه وسلم ثمانيا جميعا. وسبعا جميعا. قلت: يا أبا الشعثاء! أظنه أخر الظهر وعجل العصر. وأخر المغرب وعجل العشاء. قال: وأنا أظن ذاك.‏
Reference:
     Sahih Muslim, Book 004, Number 1521, Book: al-Salat; Page 257, #(705)-55 (Arabic version)
     Sahih Bukhari, Volume 2, Book 21, Number 270, Book: al-Tahajjud; Page 248, #1174 (Arabic version)
     Sunan al-Nisa'i, vol. 1 (كتاب المواقيت. الجمع بين الصلاتين في الحصر), from Kutayba from Sufyan from A'amru from Jabir ibn Zayd from ibn Abbas.
     Musnad Ahmad ibn Hanbal, vol 1, p221 [entire book: page 193, #1918];

'Abdullah b. Shaqiq reported: Ibn 'Abbas one day addressed us in the afternoon (after the afternoon prayer) till the sun disappeared and the stars appeared, and the people began to say: Prayer, prayer. A person from Banu Tamim came there. He neither slackened nor turned away, but (continued crying): Prayer, prayer. Ibn 'Abbas said: May you be deprived of your mother, do you teach me Sunnah? And then he said: I saw the Messenger of Allah (may peace be upon him) combining the noon and afternoon prayers and the sunset and 'Isha' prayers. 'Abdullah b. Shaqiq said: Some doubt was created in my mind about it. So I came to Abu Huraira and asked him (about it) and he testified his assertion.
Reference:
     Sahih Muslim, Book 004, Number 1523, Book: al-Salat; Page 257, #(705)-57 (Arabic version)
     Sahih Muslim, Book 004, Number 1524, Book: al-Salat; Page 257, #(705)-58 (Arabic version)

أخبرنا محمد بن عبد الأعلى قال حدثنا خالد قال حدثنا ابن جريج عن عمرو بن دينار عن أبي الشعثاء عن ابن عباس
قال صليت وراء رسول الله صلى الله عليه وسلم ثمانيا جميعا وسبعا جميعا [ش قوله (لئلا يكون على أمته حرج) أي لئلا يتحرج من يفعل ذلك من أمته وإلا فالجمع إذا حملنا على الجمع فعلا كما سبق فهو جائز لهم على مقتضى تحديد الأوقات لأن كلا من الصلاتين في وقتها إلا أن الأولى في آخر الوقت والثانية في أول الوقت].
Reference:
     Sunan al-Nisa'i, vol. 1 (كتاب المواقيت. الجمع بين الصلاتين في الحصر)
     Mu'ujam al-Tabarani al-Kabeer, by Imam al-Tabarani ( باب الظاء. أحاديث عبد الله بن العباس بن عبد المطلب بن هاشم بن عبد مناف. أبو الشعثاء جابر بن زيد عن ابن عباس.)
     Musnad Ahmad ibn Hanbal, vol 1, p273 [entire book: page 230, #2465]; vol 1, p285 [entire book: page 239, #2582]; vol 1, p366 [entire book: page 299, #3467]

Muslim in his Sahih, Ahmad ibn Hanbal in his Musnad and al-Bayhaqi in his Sunan reported:

خطَبَنا ابن عباس يوماً بعد العصر حتى غربت الشمس وبَدَت النجوم. وجعل الناس يقولون: الصلاة.قال: فجاءه رجل من بني تميم لا يفتر ولا ينثني: الصلاة الصلاة. فقال ابن عباس: أتعلّمني بالسُّنّة ؟ لا أم لك. ثم قال: رأيت رسول الله صلى الله عليه وسلم جمع بين الظهر والعصر، والمغرب والعشاء. قال عبد الله بن شقيق: فَحَاك في صدري من ذلك شيء، فأتيت أبا هريرة، فسألته فصدَّق مقالته

Conclusion
Some scholars accept the combination of prayers when there is a genuine excuse, while others maintain that this practice is permitted with or without any excuse because Allah did not want to burden us.

You have read the traditions. They are in the Sunni and Shia'a sources. Some show that the prophet combined the prayers when he had an excuse (travelling, danger, fear, rain, etc...). But they also show that the prophet performed the same practice while he was in Medina, under no fear, danger, rain, etc...

Is it not clear enough that this practice was permitted by the prophet and performed by the companions? Why deny this fact? Is it not more convenient to combine the prayers, especially when we are busy working 8 hours or more a day. Is it not less burden on us? Are we not more likely to continue praying when we can combine these prayers? Some scholars refute this proven Sunna based on personal opinion and imagination! Some argue that the prophet delayed the Zuhr prayer, and by the time he finished it, the time of the A'asr prayer started, therefore he prayed it, but did not intend to combine the 2 prayers. They just appeared to be so. If this is the argument of a scholar, then we are in the path of misguidance if we follow such scholar. Religious verdicts are not based on personal views, but they are based on the Quran and the Sunnah of the prophet! It will be so relieving if the scholars were to admit to the general public that the combination of the prayers is an authentic Sunnah and not an innovation.

Feel free to ponder more on this topic.