Is it permissible to pray in a mosque whose administrator legalizes usury and rejects the fatwas of scholars, while the Imam makes many mistakes in reciting the Qur'an and does not attend Fajr prayer, taking into account the fatwa of one of the shaykhs that one should not pray behind him or in that mosque?

It is well-known that riba (usury/interest) is forbidden in Islam. However, scholars have permitted it in cases of extreme necessity, as defined in Fatwa No. 45803. If a person commits riba due to a recognized necessity, there is no blame on him; otherwise, he must repent.

Praying behind the mosque's imam is permissible, but it is better to pray behind someone else if possible, to avoid the scholarly disagreement regarding the imamate of a fasiq (transgressor/sinner). The mosque's imam must enjoin good and forbid evil to the best of his ability.

Regarding errors in recitation during prayer: If the errors are in memorizing the Quran, but not in Al-Fatiha, the prayer is valid, and these errors can be corrected through revision. However, if the error is a grammatical mistake (lahn) that alters the meaning: if it occurs in Al-Fatiha, prayer behind him is not valid (Fatwa No. 66206). If it occurs in other parts of the prayer and was not intentional, the prayer is valid. But if the lahn was intentional, his prayer is not valid, nor is the prayer of those behind him. It is better to put forward the one who recites the Quran best, based on the saying of the Prophet (peace be upon him): "The people should be led in prayer by the one among them who is most skilled in reciting the Book of Allah."

The imam being late for Fajr prayer due to an excusable sleep does not undermine his imamate. However, if it is due to negligence, he should not be put forward, though prayer behind him remains valid (Fatwa No. 38885).