Sayyiduna Anas bin Malik (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) came to Khaybar and arrived at night. Whenever he (peace and blessings be upon him) came to a people at night, he would not attack before morning. When morning came, the Jews came out with their farming tools, and when they saw his (peace and blessings be upon him) army, they said: "By Allah! Muhammad and his army!" He (peace and blessings be upon him) said: "Allah is the Greatest! Khaybar is ruined, that is, its inhabitants. When we come upon a people in the morning, evil is the morning of those who were warned. [Surah al-Saffat: 177]"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18097