As salamu alaykum, If little time is left and someone is not shure whether he will have completed Fajr before its expiry time (i.e. sunrise), and after he prayed he checks the time and indeed he completed before its expiry time, is his salaah correct ? To give a example, sunrise is at 08:22 and the currect time on which the salaah is about to commenced is 08:18, now the person does not know whether he will manage to complete the prayer before 08:22, but afterwards when he check he sees he has comepleted at 08:21. Thus is it a prerequisite to know that you will definitly complete the prayer before its expiry time on beforehand, like it is a prerequisite to know on before hand that a prayer time has entered before one can commence a salaat. Was salaam.

All perfect praise be to Allaah, The Lord of the Worlds.  I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is not a condition for the validity of the prayer to know that one performs all of it on time or complete it entirely before its time is over, but it is a condition for its validity to know that the time of the prayer has begun.

So, whoever wakes up for the Fajr prayer shortly before its time is over, then he is obliged to take the initiative to perform it whether he knows that he will finish it on time or that a portion of it will be performed after its fixed time is over and it is forbidden for him to deliberately delay commencing it until its fixed time is over.

For more benefit, please refer to Fatwa 84538.

Allaah Knows best.