Musnad Ahmad 307:5

Husayn narrated to us, in the explanation of Shayban, from Qatadah, who said: Anas ibn Malik narrated from Abu Talhah, who said: The Prophet of Allah, may Allah bless him and grant him peace, arrived at Khaybar in the morning, while they had taken their shovels and gone out to their fields. When they saw the Prophet of Allah, may Allah bless him and grant him peace, with the army, they retreated, turning their backs. The Prophet of Allah, may Allah bless him and grant him peace, said: "Allah is the Greatest, 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."