Musnad Ahmad 28:541

Ali ibn 'Asim narrated to us, from al-Muthanna ibn al-Sabbah, from 'Amr ibn Shu'ayb, from his father, from his grandfather, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Disbelief is disavowing a lineage, even if it is slight, or claiming a lineage that is not known."