Musnad Ahmad 32:727

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Ayyub, from Ibn Sirin, who said: I heard Anas ibn Malik saying: The Messenger of Allah (peace and blessings of Allah be upon him) reached Khaybar in the morning, and they had come out with their shovels. When they saw the Messenger of Allah (peace and blessings of Allah be upon him), they said: "Muhammad and the army." The Messenger of Allah (peace and blessings of Allah be upon him) raised his hands and 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."