Musnad Abu Ya'la al-Mawsili 129:87

'Abd al-A'la narrated to us, Mu'tamir narrated to us, from Humayd, from Anas, who said: When the Prophet (peace and blessings of Allah be upon him) would raid a people, he would not raid until it was morning. Then he would look; if he heard the call to prayer (adhan), he would refrain from them, and if he did not hear the call to prayer, he would raid them. He said: So we went out to Khaybar and reached it. When it was morning and he did not hear the call to prayer, he mounted, and I mounted behind Abu Talhah, and my feet were touching the feet of the Prophet (peace and blessings of Allah be upon him). He said: They came out to us with their baskets and their spades. When they saw the Prophet (peace and blessings of Allah be upon him), they said: "Muhammad and the army!" When the Prophet (peace and blessings of Allah be upon him) saw them, he said: "Allah is the Greatest! Khaybar is ruined. Indeed, when we descend into the courtyard of a people, evil is the morning of those who have been warned."