Is it obligatory to repeat the prayer if the worshipper discovers, after finishing it, that the direction of the Qiblah was wrong, given that he did not exert sufficient effort in determining it?

Facing the Qibla is one of the conditions for the validity of prayer, and the worshiper must ascertain the direction of the Qibla. If, after prayer, a slight deviation from the Qibla becomes apparent, the prayer is not invalidated because what is obligatory is facing the direction, not the exact Kaaba itself. However, if the deviation is significant, and the worshiper made an effort and investigated, then re-performing the prayer is not incumbent upon him, in accordance with the Almighty’s saying: (So fear Allah as much as you are able). But if he did not make an effort, then he must re-perform the prayer.