Abd-Allah ibn Ubayy (Arabic: عبد الله بن أبي بن سلول‎, died 631), also called ibn Salul in reference to his mother, was a chief of the Arab tribe Banu Khazraj and one of the leading men of Medina (then known as Yathrib). Upon the arrival of Muhammad, Ibn Ubayy became a Muslim, though the sincerity of that conversion is disputed. Because of repeated conflicts with Muhammad, Islamic tradition has labelled him a Munafiq (hypocrite) and "leader of the Munafiqun".

Ibn Ubayy was one of the chiefs of the Khazraj, who at his time were in conflict with the other major Arab tribe of the city, the Banu Aws. During the fidjar, the so-called "sacrilegious war", Ibn Ubayy had led parts of the Khazraj tribe on the first day of fighting, but held aloof on the second day. Neither did he participate in the Battle of Bu'ath, due to a quarrel with another leader over the execution of Jewish hostages. It appears that at one point during this conflict, his life was saved by his Jewish allies from the tribe of Banu Qaynuqa, as he would later exclaim: "300 soldiers armed in mail, and 400 unequipped, -- they defended me on the fields of Hadaick and Boath from every foe."