Musannaf Ibn Abi Shayba 27:663

Abdullah ibn Idris narrated to us, from his father, from Atiyyah, who said: A man called Ubadah ibn al-Samit came and said: "O Messenger of Allah, I have many allies among the Jews, and their number is great. I am disgusted by their alliance, and I disavow before Allah and His Messenger the alliance of the Jews." So there was revealed concerning Ubadah: "Your ally is none but Allah and His Messenger and those who have believed," up to His saying: "because they are a people who do not understand."