From Sahih Muslim (Hadith 63):
It is reported on the authority of Sa'd b. Abi Waqqas: Both of my ears heard the Messenger of Allah saying this: He who claimed the fatherhood of anyone else besides his real father knowingly (committed a great sin) ;Paradise is forbidden to him. Abu Bakra asserted that he too heard it from the Messenger of Allah (may peace be upon him ).
Reference: Muslim 63