The Messenger of Allah ﷺ said, "There are two dawns. As for the dawn that appears like the tail of a wolf, it does not permit the prayer, nor does it forbid food. But as for the one that spreads out across the horizon, it permits the prayer and forbids food."
قال رسول الله ﷺ: الفجر فجران، فأما الفجر الذي يكون كذنب السرحان فلا تحل الصلاة فيه، ولا يحرم الطعام. وأما الذي يذهب مستطيلا في الأفق فإنه يحل ويحرم الطعام.
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Reported by Hakim (1/191) from Abu Bakr Muhammad bin Ahmad bin Hatim al-Dar-Bardi in Marw, who said, Abdullah bin Rawh Madaini told us, Yazid bin Harun told us, Ibn Abu Dhib informed us, from Harith bin Abdul-Rahman, from Muhammad bin Abdul-Rahman bin Thawban, from Jabir, and he related it. Hakim said, "Its isnad is sahih," and it serves as a corroborating witness for the hadith of Ibn Abbas.It is also related from Ibn Abbas, who said that the Messenger of Allah ﷺ said, "Fajr is of two kinds. A Fajr during which food is forbidden and prayer is permitted, and a Fajr during which prayer is forbidden and food is permitted."Reported by Daraqutni (2185), and by Ibn Khuzayma (356, 1927), and from him Hakim (1/191), from Muhammad bin Ali bin Mihraz, originally from Baghdad but who moved to Fustat, who said, Abu Ahmad Zubayri told us, from Sufyan, from Ibn Jurayj, from Ataa, from Ibn Abbas, and he related it.Ibn Khuzayma said, "No one related this from Abu Ahmad except this Ibn Mihraz." Hakim said, "It is sahih according to the standard of the two sheikhs regarding the integrity of the narrators, though the two of them did not include it. I believe I have also seen it narrated from the hadith of Abdullah bin Walid, from Thawri, as a stopped narration." He also reported it in his Book of Fasting (1/425) and said, "This is a hadith with a sahih isnad, though the two of them did not include it." He said, "Its corroborating witness is the hadith of Samura, narrated as a raised hadith," and he related it.Daraqutni said, "No one raised it to the Prophet's level except Abu Ahmad Zubayri, from Thawri, while Firyabi and others narrated it from Thawri as a stopped narration, and the companions of Ibn Jurayj likewise narrated it from him as a stopped narration." End of quote.It is also related from Abdul-Rahman bin Aish, a companion of the Messenger of Allah ﷺ, who said, "Fajr is of two kinds. As for the one that stretches lengthwise across the sky, it does not prevent the pre-dawn meal, and prayer is not yet permitted during it. But when it spreads horizontally across the horizon, then food becomes forbidden, so pray the dawn prayer."Reported by Daraqutni (2183) from the hadith of Walid bin Muslim, from Walid bin Sulayman, who said, I heard Rabia bin Yazid say, I heard Abdul-Rahman bin Aish relate this as a stopped narration.This chain contains Walid bin Muslim, who practices the deceptive form of tadlis known as tadlis al-taswiya. However, Daraqutni said, "Its isnad is sahih," and did not fault it on account of Walid's tadlis.