Sahih Muslim Book 1, Hadith Number 121.

Chapter : The condition of the Faith of one who knowingly denies his true fatherhood.

Sa’d and Abu Bakra each one of them said: My ears heard and my hearing preserved it that Muhammad (peace and blessings be upon him) observed: He who claimed for another one his fatherhood besides his own father knowingly that he was not his father-to him Paradise is forbidden.