Ruling 962 — Prayer (Ṣalāh)

If a person has not lost hope in being able to perform prayers in a standing position by the end of the prescribed time for the prayer, in the event that he performs prayers at the beginning of the prescribed time [sitting] and he is able to stand at the end of the prescribed time, he must perform the prayer again [standing]. However, if he has lost hope in being able to perform prayers in a standing position and performs prayers at the beginning of the prescribed time [sitting] and then he is able to stand, it is not necessary for him to repeat the prayer.