Muḥammad ibn Maslama was a prominent companion of the Prophet Muḥammad who belonged to the Ḥāritha clan of the Medinan tribe of Aws. He played a key role in the events leading to the defeat of the three Jewish tribes of Medina and participated in the assassination of the Jewish leader Kaʿb ibn al-Ashraf. Muḥammad ibn Maslama was connected to the Jews in various ways, as is evident, for example, from accounts claiming that he was Kaʿb's maternal nephew, and that his clan, the Banū Ḥāritha, lived in the predominantly Jewish oasis of Khaybar for nearly a year in the pre-Islamic period. Muḥammad ibn Maslama's role in Kaʿb's assassination has recently been argued to be of dubious historicity. This article offers a reassessment of this conclusion by placing the accounts of Muḥammad ibn Maslama's ties with the Jews, on the one hand, and those that depict him as their enemy, on the other, in the broader context of the change in the attitudes of some of the Anṣār towards the Jews during the Prophet's Medinan period. It argues that this change of attitudes is an attested historical pattern and, accordingly, that the fact of Muḥammad ibn Maslama's participation in the assassination of Kaʿb ibn al-Ashraf can be deemed reliable.