Musnad Ahmad 8:59

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from 'Asim al-Ahwal, who said: I heard Abu 'Uthman, who said: I heard Sa'd—and he was the first to shoot an arrow in the way of Allah—and Abu Bakrah—who scaled the fortress of Ta'if with some people and came to the Prophet, peace and blessings of Allah be upon him—and they both said: We heard the Prophet, peace and blessings of Allah be upon him, saying: "Whoever claims to be the son of someone other than his father, while he knows that he is not his father, then Paradise is forbidden to him."