Abu Hurayrah radiallahu 'anhu related that the Prophet sallallahu 'alayhi wa sallam said: "Fast when they fast, end the fast when they end theirs, and sacrifice the day that they sacrifice." {qluetip title=[1]}Sahih: Related by at-Tirmidhi (2/37). Shaykh al-Albani authenticated it in As-Sahihah (no. 224).{/qluetip}
Al-Bayhaqi relates by way of Abu Hanifah, who said: 'Ali ibn al-Aqmar related to me, from Masruq, who said: I entered upon 'A'ishah on the day of 'Arafah, so she said: "Serve Masruq with some gruel, and make it more sweet." Masruq said: Nothing prevented me from fasting this day except that I feared that it may be the Day of Sacrifice. So 'A'ishah said to me: "The Day of Sacrifice is when the people sacrifice, and the day of ending the fast is when the people end their fast."
This chain of narration is jayyid (good) due to what has preceded.
Understanding the Hadith
Imam at-Tirmidhi says after quoting the hadith:
"One of the people of knowledge has explained this hadith by saying: Its meaning is to fast and end the fast along with the Jama'ah and the majority of people."
As-San'ani said in Subulas-Salam (2/72):
"In this (hadith) is a proof that being in agreement with the people is accepted in establishing 'Eid, and that the individual person who believes that it is the day of 'Eid - because of the sighting of the moon - then it is obligatory upon him to be in agreement with the people, and that the ruling of the people - concerning the Prayer, breaking the fast, and sacrificing - is binding upon the individual."
Ibn al-Qayyim - rahimahullah - mentioned this meaning in Tahdhib as-Sunan (3/214), and said:
"It is said: In in it a refutation of those who say that whosoever knows the positions of the moon due to astronomical calculations, then it is permissible for him to fast and end the fast, even if others do not know. It is also said: That the individual witness who sees the moon, but the qadi (judge) has not accepted his testimony, then there is no fasting for him, just as there is no fasting for the people."
Abul-Hasan as-Sindi said in Hashiyah 'ala Ibn Majah, after mentioning the hadith of Abu Hurayrah which was related by at-Tirmidhi:
"And its apparent meaning is: That there is no room for individual (opinions) to enter into these affairs, nor to act individually in this. Rather, this affair goes back to the Imam (the Leader of the Muslims) and the Jama'ah (united body of Muslims under the Imam). It is obligatory upon the individuals to follow the Imam and the Jama'ah. From this is that is an individual sights the moon, but the qadi rejects his witness, then the individual has no right in these matters, but rather he must follow the Jama'ah in this."
And this is the meaning which is evident from the hadith, and which is emphasised by the fact that 'A'ishah radiallahu 'anha used it with Masruq when he prevented himself from fasting on the day of 'Arafah, fearing that it could be the Day of Sacrifice. So she explained to him that there is no weight given to his individual opinion in this, and that he should follow the Jama'ah. So she said to him: "The Day of Sacrifice is when the people sacrifice, and the day of ending the fast is when the people end their fast."
And this is what is befitting for the easy-natured and tolerant Shari'ah (Prescribed Islamic Law), one of the goals of which is uniting the people together, unifying their ranks and keeping away from them all that would split their comprehensive unity - from the individual opinions. So the Shari'ah does not give any weight to the individual opinion in matters concerning 'ibadah jama'iyyah (collective acts of worship), such as Fasting, 'Eid and Prayer in congregation - even if the opinion is correct, from one angle. Do you not see that the Sahabah (the Companions) - radiallahu 'anhum - used to pray behind each other. So from them were those who held the view that touching a woman, or the flowing of blood from the body invalidates the wudhu' (ablution), along with those who did not hold this view. From them were those who would complete the Prayer whilst traveling, whilst others shortened. Yet these, and other such differences, did not prevent them from collectively praying behind a single Imam and deeming it to be acceptable. And this is because they knew that tafarruq (splitting-up) in the Religion is more evil than having ikhtilaf (differences) in some opinions. Indeed, the matter with one of them reached the extent that he would not even deem acceptable any opinion which differed with the great Imam in the major gatherings; such as the gathering at Mina (during Hajj), to the extent that he would totally abandon acting upon his opinion in that gathering - fleeing from that which could result from this evil, because of acting according to his own opinion.
Thus, Abu Dawud relates (1/307) that 'Uthman radiallahu 'anhu prayed four raka'at at Mina, so 'Abdullah ibn Mas'ud critisised him saying: "I prayed two raka'at with the Prophet sallallahu 'alayhi wa sallam, and two raka'at with Abu Bakr, and two raka'at with 'Umar, and two raka'at with 'Uthman in the beginning of his rule, then he completed it (i.e. by praying four raka'at). After that the ways became divided with you all. So I hope from these four raka'at, that two of them would be accepted." Then Ibn Mas'ud prayed four raka'at. So it was said to him: You criticised 'Uthman, yet you prayed four? So he said: "Differing is evil."
Its chain of narration is Sahih (authentic), and something similar to this is related in the Musnad (5/155) of Imam Ahmad, from Abu Dharr radiallahu 'anhum ajma'in.
So those who continue splitting-up with regards to the Prayer, and who refuse to follow the local Imams in some mosques - especially in the witr Prayer during Ramadhan - using as proof that this is against their madhhab (school of thought), then they should reflect upon the above mentioned hadith and athar (narration). Likewise, those who claim knowledge of astronomy and who, due to their opinion, fast and end their fast alone - preceding or lagging behind the majority of Muslims, not seeing any problem in doing so - should also reflect upon the previously quoted proofs. So all of them should consider, and reflect upon the knowledge that has been mentioned. Perhaps they will find for themselves a cure for their ignorance and self-delusion, so that they may then become a unified rank along with their Muslim brothers - for indeed the Hand of Allah is over the Jama'ah.
(s) Silsilat al-Ahadith as-Sahihah (1/442-445), the hadith authentications have been abridged and edited.