Sayyiduna Abdullah bin Abi Awfa (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) attacked Khaybar while those people were unaware at that time. They said: "Muhammad (peace and blessings be upon him) has come, and the army is with him too." The Prophet (peace and blessings be upon him) said: "Allahu Akbar! Khaybar is ruined! When we descend upon the courtyard of a people, evil is the morning of those who have been warned."
Al-Tabarani recorded it in al-Mu'jam al-Saghir and al-Mu'jam al-Awsat; its chain contains Abdullah bin Muhammad bin al-Mughirah, who is da'if (weak).