What is the ruling on an adult foundling attributing himself to his foster parent?

It is not permissible for a foundling or anyone else to attribute himself to other than his father, because the Prophet, peace and blessings be upon him, said: "No man who knowingly claims another as his father, other than his true father, has committed an act of disbelief. And whoever claims kinship with people to whom he does not belong, let him take his seat in Hellfire." Loyalty and appreciation to his foster parent should be shown by honoring them and consistently treating them well, not by what Allah has forbidden.