Wa alaykum. All Muslims agree that there are five mandatory prayers
throughout the day and night. They also agree that these
five daily prayers have specific times in which they must be
performed, and that combining the prayers is, at least,
sometimes permissible (saying the dhuhr (noon) prayer
then immediately followed by the asr (afternoon) prayer, or
saying the maghrib (post-sunset) prayer then immediately
followed by the isha (night) prayer). The Maliki, Shafi’i,
and Hanbali schools of thought agree that combining of the
prayers while traveling is permitted, but they do not allow
combining of the prayers for other reasons. The Hanafi
school of thought permits combining of the prayers only on
the day of Arafat. Whereas the imami Shia school of
thought, allows combining of the prayers in all cases—
while traveling or not, for any or no other specific reason,
during war and peace, while the weather is rainy or not, and
so on. The real dispute is as to when the exact beginning
and end of the prayer times are. Thus, the dispute must be
referred to the Holy Quran and narrations of the Holy
Prophet Muhammad.
Three verses in the Holy Quran speak of the times for
the prayers. Allah, the Exalted says, “Perform the prayers
from the mid-day till the darkness of the night, and recite
the Quran in the early dawn. Verily, the recitation of the
Quran in the early dawn is ever-witnessed.” (Quran 17:78) “Mid-day” refers to the shared time for the dhuhr and asr prayers, “the darkness of the night” refers to the shared time of the
mahrib and isha prayers, and “early dawn” refers to the fajr
(dawn) prayer. The Holy Quran clearly and simply states
that there are three main times for the five daily prayers.
Although the prayers are five, still they fall into three main
periods of time. The great Sunni scholar, Fakhr al-Din al-
Razi understood this interpretation from this verse also. (Fakhr al-din al-Razi, Tafsir. Vol. 5. 428.) Of course, the prayers must be done in order; the dhuhr prayer must be performed before the asr prayer, and the maghrib prayer must be performed before the isha prayer.
The Holy Quran also says, “And perform the prayers at
the two ends of the day, and in some hours of the night.
Verily, the good deeds remove the evil deeds. That is a
reminder for the mindful.” Quran 11:114
Muslim jurists and Quran commentators agree that this verse refers to the five compulsory prayers, as the Holy Quran states, it determines the timing of the prayers—the three main times; two of
them at the “ends of the day” and the third in “some hours
of the night.” The first, “ends of the day” is the time of the
morning prayer, the second, “ends of the day” begins at
noon and ends at sunset (making this the time for the dhuhr
and asr prayers), and the “hours of the night” is the third
main time in which the maghrib and isha prayers should be
said; these prayers extends from the beginning of the night
until midnight.
A similar division of times is expressed in a third verse,
“So bear with patience (O Muhammad) all that they say,
and glorify the praises of your Lord before the rising of the
sun, and before its setting, and during a part of the night, also glorify His praises, and so likewise after the
prayers.” Quran 50:39-40
As in the previous verse, the jurists and the commentators also agree that this verse refers to the times of the five mandatory prayers; in addition to, dividing the time for the prayers into three segments: first, the time from dawn until sunrise which is the time for the dawn prayers (fajr); second, the time from noon until sunset, which is the time for the noon and afternoon prayers; and third, the “part of the night” which extends from after sunset till midnight, which is the time for the evening and night prayers.
Referring to the last part of the cited verse (50:39-40),
“And so likewise after the prostration,” according to the
commentators, it refers either to the nawafil (recommended) prayers or specifically to salat al-layl (the midnight prayer) which are among the highly recommended prayers.
Imam al-Bukhari and others report that the Holy
Prophet used to combine his prayers into three sections of
time, “The Messenger of Allah observed the noon and
afternoon prayers together and the sunset and night prayers
together without being in a state of fear or journeying.” Sahih al-Bukhari. “Book on Times of Prayers.” Hadith 510 and 529. “Book on Friday Prayer.” Hadith 1103. Sahih Muslim. “Book on the
Prayer of Travelers.” Hadith 1146. al-Tirmidhi, “Book on Prayer.”
Hadith 172. al-Nisa’i. “Book on Timings.” Hadith 585, 597-599. Abu Dawud. “Book on Prayer.” Hadith 1024, 1025, and 1027. Musnad Ahmad ibn Hanbal. Vol. 1:217, 221, 223, 251, 273, 283, 285, 346, 349, 351, 354, 360, and 366. Malik, “Book on Shortening the Prayer While Traveling.” Hadith 300.
Imam Muslim narrates the same hadith and adds that when
the Holy Prophet was asked by Ibn ‘Abbas why he
authorized combining of the two prayers, the Holy Prophet replied that he did not want to cause difficulty for his
nation. Sahih Muslim, “Book of the Prayers of Travelers.” Ch. 6. Hadith 50-54.
In the same book, ibn ‘Abbas himself narrates
that they used to combine the two prayers during the time
of the Holy Prophet.172 Therefore, both the Holy Quran and
the tradition of the Holy Prophet indicate clear authorization and permission to combine the two prayers without any particular reason. It also asserts that Allah the Merciful made His religion easy for the believers.
This is quoted from the book Inquiries about Shia Islam 2nd Edition by Sayed Mustafa Qazwini pages 87-90
In the last paragraph where it says 172 this was a footnote for a hadith Sahih Muslim ch 6-8 hadith 58-62