The fabrication of a distinctly prestigious genealogy was among the measures adopted by the Banū Naṣr to justify their right to govern al-Andalus. Several Arabic textual and epigraphic sources emphasise the Anşārī family origins of the Naşrids, connecting them with Sa‘d b. ‘Ubāda (d. 14/635). This chapter's aim is to trace, link by link, the connection of the eastern Anşār with the Banū Naşr from the sixth to the thirteenth centuries, in order to demonstrate the impossibility of reconstructing a complete genealogical chain, and, therefore, the lack of veracity of the Banū Naşr assertion which effectively legitimated the Naşrid dynasty. Attention will also be paid to the attempted Naşrid claim to the caliphate, a legitimist intention that seems to be confirmed by virtue of having chosen Sa‘d b. ‘Ubāda as their ancestor, since this figure was proclaimed caliph by his tribe upon the death of the prophet Muḥammad.