What is the ruling on buying a bird that has been caught and is being sold by a person who does not fear God and does not inquire about the ruling of religion concerning that?

The fundamental principle is the presumption of innocence. If a person hunts a bird or catches it, there is no religious impediment to buying it, unless you know or suspect something is amiss concerning it. However, if you know that the person is untrustworthy or that the bird is stolen, then it is not permissible for you to buy it. Anything purchased that is stolen must be returned to its owner if he is known, and the buyer may then reclaim the price from the thief. It is not permissible for the buyer to benefit from it after knowing it is stolen. This is based on the saying of the Prophet, peace and blessings be upon him: "If a man's property is stolen or lost, and he finds it in the possession of a specific person, then he has a greater right to it, and the buyer may reclaim the price from the seller."