What is the ruling on praying in a mosque whose Qiblah is deviated by 44.5 degrees to the north, given that its imam is more pious than the imam of another mosque whose Qiblah is correct? What is the degree of deviation from the Qiblah that invalidates prayer? Is it permissible to pray in it, following its imam, to attain the reward of congregational prayer? Is it obligatory to face the Qiblah when performing voluntary prayers?

There is no disagreement among scholars that facing the Qibla is a condition for the validity of the obligatory prayer when one is able to do so. The aforementioned mosque is significantly deviated from the Qibla, so prayer in it is not permissible because it lacks one of the conditions for its validity, which is facing the Qibla. As for voluntary prayers, facing the Qibla is as obligatory for them as it is for obligatory prayers, unless the Muslim is traveling, in which case it is permissible for him to pray them on his mount, not facing the Qibla, based on the saying of Ibn Umar (may Allah be pleased with them both): "The Messenger of Allah (peace be upon him) used to pray voluntary prayers on his mount in whatever direction it faced, and he would pray Witr on it, but he would not pray the obligatory prayers on it."