One common question in Islamic jurisprudence is whether a prayer becomes invalid if its designated time expires before it is completed. Scholars are in consensus that, except for the Fajr (morning) prayer and the Jumu’ah (Friday) prayer, the expiration of a prayer’s time does not invalidate it.
For the Fajr prayer, however, Imam Abu Hanifa holds a unique position. He argues that if the sun rises while one is still performing the prayer, it becomes invalid, based on hadiths that prohibit praying during sunrise. On the other hand, Imam Abu Yusuf and Imam Muhammad maintain that if the final sitting (tashahhud) has been completed before the sun rises, the prayer remains valid (refer to Kasani, Bada’i, 1/122-124; Ibn al-Humam, Fath al-Qadir, 1/386).
The other schools of thought base their rulings on a hadith from the Prophet Muhammad (peace be upon him): “If one rak‘ah of the Fajr prayer is performed before sunrise, or one rak‘ah of the Asr prayer is performed before sunset, the prayer is valid and may be completed” (Bukhari, Mawaqit al-Salah, 28 [579]). These schools affirm that the expiration of a prayer’s time while performing it does not invalidate the prayer (refer to Ibn Rushd, Bidayat al-Mujtahid, 1/102-103; Ibn Qudamah, Al-Mughni, 1/273).
Thus, while there is a difference of opinion regarding the Fajr prayer, the general ruling is that if the time for a prayer ends while it is still being performed, the prayer does not become invalid.