Musannaf Ibn Abi Shayba 28:632

Ya'la ibn 'Ubayd narrated to us, from Muhammad ibn 'Amr, from Sa'id ibn al-Mundhir, who said: The Messenger of Allah (may Allah bless him and grant him peace) went out to Uhud. When he passed the mountain pass of al-Wada', he looked behind him and saw a handsome battalion. He said, "Who are these?" They said, "Abdullah ibn Ubayy ibn Salul and his allies from the Jews." He said, "Have they accepted Islam?" They said, "No." He said, "Then we do not seek the help of the disbelievers against the polytheists."