The Messenger of Allah ﷺ said, "Pray the dawn prayer when the morning light appears, for that brings greater reward."
قال رسول الله ﷺ: أصبحوا بالصبح، فإنه أعظم لأجوركم.
Reported by Abu Dawud (424), Tirmidhi (154), Nasai (548, 549), and Ibn Majah (672), all of them through various chains from Asim bin Umar bin Qatada, from Mahmud bin Labeed, from Rafi bin Khadij, who mentioned the same thing. The wording given is that of Abu Dawud, while the wording of Tirmidhi and Nasai is, "Delay Fajr until it grows light, for that carries greater reward." Tirmidhi said, "The hadith of Rafi bin Khadij is a hasan sahih hadith. A number of scholars among the companions of the Prophet ﷺ and the successors held the view that Fajr prayer should be delayed until it grows light, and this is the view of Sufyan Thawri. Shafii, Ahmad, and Ishaq said that the meaning of 'isfar' (growing light) is that dawn should become clearly visible beyond doubt, and they did not hold that its meaning was to delay the prayer itself." End of quote.His statement "yadih" comes from "wadaha," meaning dawn has become visible, as one says "the dawn became clear" when it grows bright. The apparent meaning of this hadith conflicts with the sahih hadiths concerning performing Fajr prayer in the darkness before dawn, so scholars have offered several responses to this, one of which is what Tirmidhi mentioned.Another response is what Tahawi mentioned in Sharh Maani al-Athar (1/184), "What is proper is to enter into Fajr prayer at the time of darkness and to finish it at the time when light has appeared, in agreement with what we have related from the Messenger of Allah ﷺ. This is the view of Abu Hanifa, Abu Yusuf, and Muhammad, may Allah have mercy on them all." This was countered by the fact that Ayesha said, "The women would leave wrapped in their garments, unrecognizable due to the darkness."Another response is what Hafiz bin Qayyim mentioned in Ilam Muwaqqieen, "This, once established, is only meant to refer to lengthening the prayer into the period of light, not to beginning it then. So one would enter the prayer while it is still dark and come out of it once it has grown light, just as the Prophet ﷺ used to do. His statement thus agrees with his practice rather than contradicting it. How could one imagine that he would persistently do something when the greater reward lay in doing the opposite?" End of quote. This is close to what Tahawi said.Another response is that the statement "Delay Fajr until it grows light" has been transmitted according to its meaning, and the original wording was "perform the prayer when dawn breaks," as in the narration of Abu Dawud. Jazari said, meaning, "Pray it at the break of dawn. One says a man has 'entered the dawn' when dawn has come upon him." End of quote. Suyuti said in his marginal notes on Nasai, "From this it is known that the narration of whoever related this hadith with the wording 'Delay Fajr until it grows light' conveyed it according to its meaning, and that it is evidence for the superiority of praying it in the darkness before dawn, not for delaying it until the light appears." End of quote. See Miraat Masabih (1/322).Another response is that when they were commanded to hasten the prayer, some of them understood this to refer to the first, false dawn, so they were then commanded to delay it until the second, true dawn, which is the actual time of Fajr prayer.Another response is that what is meant refers to a moonlit night, since in such a night the true dawn is not clearly distinguishable because of the moonlight, so they were commanded to wait for the light of dawn itself, meaning the actual break of day, as Ibn Hibban stated in his Sahih (4/358-359), saying, "By his statement 'Delay it until it grows light,' the Prophet ﷺ meant on moonlit nights, when the emergence of the true dawn is not clearly apparent, so that a person would not perform the dawn prayer except after being certain that dawn had actually broken through the appearance of light. For if the prayer is performed as we have described, it carries greater reward than if it were performed without certainty that dawn had actually broken." End of quote.One must accept one of these interpretations so that the practice of the Messenger of Allah ﷺ does not contradict his statement. This hadith also shows that the Messenger of Allah ﷺ would sometimes begin and finish the Fajr prayer while it was still dark, as Ayesha described, and at other times he would begin it while it was dark but prolong the recitation so that he would finish once it had grown light, as in the hadith of Abu Barza Aslami and the hadith of Anas.A note, the hadith of Rafi bin Khadij is the most sahih of what has been related concerning delaying the prayer until it grows light. What has been related from Bilal, Qatada bin Numan, Ibn Masud, Abu Hurairah, and Hawwa Ansariyya, some of it traces back to the hadith of Rafi bin Khadij, while the rest cannot be relied upon as proof due to weakness in it. For more, see Nasb Raya (1/235).