What is the ruling of the Sharia on a man who gave his son as a gift to his brother, who is unable to have children, so the son became known by his uncle's name?

It is impermissible by consensus for a man to give his son to his brother for adoption, attributing him to him, as this explicitly contradicts the Qur’an. However, if the child truly remains attributed to his father, there is no harm in his uncle being referred to by his kunya (agnomen), nor is it a condition for one who is given a kunya to have children. Indeed, Aisha, may Allah be pleased with her, was given the kunya Umm Abdillah even though she had not given birth, and similarly, the Prophet, peace and blessings be upon him, gave the kunya Abu Umayr to the young boy.