It is narrated from Hazrat Anas bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) set out for Khaybar in the morning. The people were out working at that time. They began to say, "Muhammad and his army have come," and then they started running towards their fort. The Prophet (peace and blessings be upon him) raised his hands and said "Allahu Akbar" three times and said, "Khaybar is destroyed. When we descend into the courtyard of a people, the morning of those who have been warned is the worst morning."