All Muslims agree that the timeframe for the Fajr prayer is from dawn to sunrise.
In his encyclopedic legal reference al-Mughnī, Ibn Qudāmah asserts that there is scholarly consensus (ijmā`) that the time for the Fajr prayer commences with the arrival of the true dawn. The true dawn can be distinguished from the false dawn in that it appears as a clear white line along the horizon.
The time for the Fajr prayer comes to an end with the start of sunrise. The evidence for this is as follows:
The Prophet (peace be upon him) said: “The time for the morning prayer is from the arrival of dawn up until sunrise.” [Sahīh Muslim (173)]
He also said: “Whoever offers one unit of the morning prayer before sunrise has achieved the morning prayer.” [Sahīh al-Bukhārī (579) and Sahīh Muslim (608)]
Sunrise is defined at the time when the disk of the Sun begins to emerge over the horizon.
Once, someone came to the Prophet (peace be upon him) and asked about the timeframe of the prayers. The Prophet (peace be upon him) did not give him any answer (as he preferred to demonstrate the answer by action). He ordered Bilāl to offer the call for the Fajr prayer so that it could be performed at the crack of dawn. The people could barely make out each other’s features. On the following day, he delayed Fajr so much that, when the people had finished praying, someone commented that the Sun was rising or was just about to rise. Then he summoned the questioner and said: “The timeframe for the prayers is between these two times. [Sahīh Muslim (614)]
This hadīth is quite long and discusses how the Prophet (peace be upon him) demonstrated the times of all five prayers in this way. I have sufficed here with mentioning what relates to the Fajr prayer.
Anyone who offers the Fajr prayer within this timeframe has offered the prayer on time.
The best time to offer the prayer
Scholars have expressed differing opinions as to the best time to offer the Fajr prayer. This is due to their different ways of understanding the following hadith:
Prophet Muhammad (peace be upon him) said: “Offer the Fajr prayer in the light of the morning, for this is greater for your reward.” [Sunan al-Tirmidhī (154)]
This is an authentic hadīth, and this has been demonstrated by Ibn al-Qattān [Bayān al-Wahm wa al-Ihām (2512)] and Ibn Taymiyah [Majmū` al-Fatāwā (22/97)]
This hadith clearly refers to the preferred time to offer the Fajr prayer. Scholars disagree as to how it should be interpreted.
The view of Abū Hanifah and the Hanafī school of law is that it is preferred to postpone the prayer until the sky becomes light. They tale the hadith on face value.
The majority of scholars, on the other hand, are of the view that it is a preferred sunnah to offer the Fajr prayer at the beginning of its time, before the darkness of the night is dispelled.
They cite as evidence that `A’ishah said: “We, the believing women, performed our Fajr prayer along with the Prophet (peace be upon him) wrapped up in their shawls. Then they would depart for their homes as soon as they completed their prayers without being able to recognize one another because of how dark it was. [Sahīh al-Bukhārī (578) and Sahīh Muslim (645)]
This indicates that the prayer should be performed early. This is the view of Mālik, Shāfi`ī, and Ahmad and their respective schools of thought.
There are two ways that the majority of scholars respond to the apparent meaning of the hadīth: ““Offer the Fajr prayer in the light of the morning.”
1. What is meant by offering the prayer in the “light of the morning” is the time when the prayer should be completed. This means that the hadīth is encouraging us to prolong our morning prayers so that by the time we finish them it has already started to grow light outside.
This interpretation is supported by the hadīth related by Abū Barzah al-Aslamī where he says: “Allah’s Messenger (peace be upon him) used to turn to finish his morning prayers at a time when a person could recognize the person who was sitting next to him. He would recite between 60 and 100 verses.” [Sahīh al-Bukhārī (547) and Sahīh Muslim (647)]
2. It is possible that what the Prophet (peace be upon him) meant by it was to wait until it was certain that dawn had arrived and not start the prayer on the basis of an assumption. The Prophet (peace be upon him) always waited until it was verified with certainty that dawn had arrived except on one occasion when he was in Muzdalifah when he prayed it earlier than was his habit. In this case “light of the morning” simply means when you can clearly see a thin line of light on the horizon and know for certain that dawn has truly arrived.
In light of all the evidence taken together, the strongest opinion is that of the majority, that the prayer should be prayed as early in the morning as possible.
And Allah knows best.