Musnad Abu Ya'la al-Mawsili 3:63

Ubayd Allah narrated to us, al-Dahhak ibn Makhlad narrated to us, Sufyan narrated to us, from Muhammad ibn al-Sa’ib, from Asbagh ibn Nubatah, from Ali, that he said: "The Prophet, may Allah bless him and grant him peace, made a peace treaty with the Banu Taghlib on the condition that they remain upon their religion and that they do not baptize their children. They have violated [the treaty], and if the matter is completed for me, I will kill the fighting men and take the offspring captive."