Is it permissible to pray in a mosque that was built, and it later became apparent that its qiblah has a significant deviation, and what is the ruling on the previous prayers performed therein?

Facing the Qiblah is a condition for the validity of prayer, except in three cases: fear during battle, supererogatory prayers while riding an animal, and incapacitation. One who can see the Kaaba should face its exact location, while one who is far from it should face its general direction. If the deviation is minor and does not go outside the general direction, it does not harm the prayer. However, if it is significant, the prayer is invalid. Past prayers are valid as long as diligence was exercised in facing the Qiblah, and the error was later discovered; there is no need to repeat them.