Is it permissible to inquire about the religious state of a deceased Muslim before praying over them, and if they were a fasiq (transgressor), why do we pray over them and supplicate for mercy for them, and why do we not leave them to Allah's command without our supplication for them?

Whoever's Islam has been established and nothing has invalidated it, he is a Muslim, and prayers should be offered for him and supplications for forgiveness and mercy should be made for him, even if he was a profligate, for he is more in need of supplication. Allah has only forbidden seeking forgiveness for polytheists. It is not appropriate to inquire about the deceased's religious affairs, because a Muslim is commanded to conceal the faults of his brother. The Prophet, peace and blessings be upon him, did not inquire about anything concerning the deceased except debt due to its grave importance. So, he would pray over those who left behind repayment for their debt and command the Companions to pray over those who did not leave behind repayment. Then, after the conquests, he began to bear the debt of the debtor and pray over him, as he said: "I am more deserving of the believers than they are of themselves. So, whoever among the believers dies and leaves behind a debt, its repayment is upon me, and whoever leaves behind wealth, it is for his heirs." The Prophet, peace and blessings be upon him, used to refrain from praying over one who owed a debt to encourage people to pay their debts.