Two of the pagan Arabian tribes that resided in Yathrub, on the outskirts of Madina, where the three 'Jewish' tribes of Nadir, Qaynouqa and Quraydha lived. The latter three, were actually Arab tribes who had willingly converted to the religion of the Jews and, who had intermarried with the original immigrant Jews. They were Arab in their tribal structure, their language, their names and in their general conduct.
In his introduction to the 'Life of Muhammad', A. Guillaume mentions a report by (ibn Hisham 288,293, 299) in which Muhammad speaking to Abbas calls the Aus and Khazraj "ůmy and your maternal uncles".
In Ibn Ishaq's 'Sira' (p:197), there are several reports about the very close tribal inter relationships between the Judaized Arabs and their pagan brothers and sisters.
Because these two tribes had been exposed over a very long period of time to the monotheism of the 'Jews' and their stories, both were much more easily inclined to accept Muhmmad's message than his own Quraysh tribe.