What is the ruling on a domestic bird that was purchased for a high price from someone who found it in the street? Is the buyer considered sinful, and what should he do if that is the case?

If a domestic bird is found in the street, it falls under the ruling of a 'luqatah' (found item). The one who finds it has three options: to eat it and guarantee its value to its owner, or to keep it and spend on its upkeep, or to sell it and keep its price for its owner. It becomes the property of the finder after one year of public announcement. Buying from the one who found the bird is permissible, and there is no sin in it. However, if the seller bought it from an unknown person, the principle is that whatever is in a person's possession is their property unless they are accused of theft, and therefore, the purchase is valid.