Musnad Ahmad 307:2

Rawh narrated to us, Sa'id ibn Abi 'Arubah narrated to us, from Qatadah, from Anas ibn Malik, from Abu Talhah, who said: When the Prophet of Allah, peace and blessings of Allah be upon him, reached Khaybar in the morning, they had taken their shovels and gone out to their fields and their land. When they saw the Prophet of Allah, peace and blessings of Allah be upon him, with the army, they retreated, turning their backs. The Prophet of Allah said: "Allah is the Greatest, Allah is the Greatest. Indeed, when we descend into the courtyard of a people, evil is the morning of those who have been warned."