The Prophet ﷺ once slept past the two units of prayer before dawn, so he made them up after the sun had risen.
أن النبي ﷺ ينام عن ركعتي الفجر فقضاهما بعد ما طلعت الشمس.
Ibn Majah (1155) narrated it from Abdul-Rahman bin Ibrahim and Yaqub bin Humayd bin Kasib, who both said, Marwan bin Muawiya told us, from Yazid bin Kaysan, from Abu Hazim, from Abu Hurairah, who said, then he mentioned it. Its isnad is hasan because of Yazid bin Kaysan, who is among the narrators of Muslim, though he is disputed, but his hadith is hasan.Ibn Hibban narrated it in his Sahih (2652) through another route from Marwan bin Muawiya with the same wording. The origin of the hadith is in Sahih Muslim (680/310), from Yahya bin Saeed, from Yazid bin Kaysan, with the same chain, concerning the story of the Prophet's ﷺ falling asleep during a journey until the sun rose, and it states, "and he performed two prostrations, then the prayer call was made and he prayed the morning prayer." This has already passed in the Book of Adhan.Tirmidhi (423) narrated it from Uqba bin Mukram Ammi Basri, who said, Amr bin Asim told us, Hammam told us, from Qatada, from Nadr bin Anas, from Bashir bin Nuhayk, from Abu Hurairah, who said, the Messenger of Allah ﷺ said, "Whoever does not pray the two rakats of Fajr should pray them after the sun has risen."Tirmidhi said, "We do not know this hadith except from this route. It has been reported that Ibn Umar used to do this. This is the practice followed by some scholars, and it is the view held by Sufyan Thawri, Ibn Mubarak, Shafii, Ahmad, and Ishaq." He said, "We do not know of anyone who narrated this hadith from Hammam with this isnad in this manner except Amr bin Asim Kilabi. What is well known from the hadith of Qatada, from Nadr bin Anas, from Bashir bin Nuhayk, from Abu Hurairah, from the Prophet ﷺ, is that he said, 'Whoever catches one rakah of the morning prayer before the sun rises has caught the morning prayer.'"Shaykh Ahmad Shakir responded to this by saying that these are two separate hadiths, and that Amr bin Asim Kilabi is a trustworthy and reliable narrator, so his being alone in narrating this report does not harm its standing. Hakim narrated it (1/247) through the route of Amr bin Asim with the wording, "Whoever does not pray the two rakats of Fajr before the sun rises should pray them," and he graded it sahih according to the standard of the two Shaykhs (Bukhari and Muslim). He also narrated it again with a similar wording (1/306) and graded it sahih. The commentator noted that Daraqutni also narrated it. End of quote.Ibn Khuzayma graded it sahih (1117), narrating it through the route of Amr bin Asim, with the wording, "Whoever forgets the two rakats of Fajr should pray them when the sun rises."