If it is impermissible to adopt a foundling of unknown parentage and attribute him to his sponsor, then to whom should he be attributed?

If a foundling's father is unknown and no one claims his lineage, then he is not attributed to anyone. Instead, he should be called a brother in faith, in accordance with the verse: ﴿Call them by [the names of] their fathers; it is more just in the sight of Allah. But if you do not know their fathers, then they are your brothers in religion and your allies.﴾ The Prophet, peace and blessings be upon him, warned against attributing oneself to other than one's father, as he said: "Whoever claims to be the son of someone other than his father, while knowing it, Paradise will be forbidden for him." There is no harm in choosing a general name for him, such as so-and-so son of Abdullah.