The Prophet ﷺ reached Khaybar in the early morning. The people had already come out carrying their spades on their shoulders. When they saw him, they cried out, "This is Muhammad and his army! Muhammad and his army!" and they fled to take refuge in their fortress.The Prophet ﷺ raised his hands and said, "Allah is the Greatest! Khaybar is destroyed! When we descend upon the territory of a people, evil is the morning of those who have been warned."The hadith continues.
صبح النبي ﷺ خيبر وقد خرجوا بالمساحي على أعناقهم فلما رأوه قالوا: هذا محمد والخميس، محمد والخميس فلجؤوا إلى الحصن، فرفع النبي ﷺ يديه، وقال: الله أكبر خربت خيبر إنا إذا نزلنا بساحة قوم فساء صباح المنذرين. الحديث
Bukhari related it in the Book of Jihad and Expeditions (2991), and Muslim related it in the Book of Hunting and Slaughtered Animals (1940), both of them by way of Ayub, from Muhammad (that is, Ibn Sirin), from Anas, who mentioned it. The wording given is Bukhari's. Muslim also related it in the Book of Marriage (1365:84) by way of Ismail bin Ulaya, from Abdul-Aziz, from Anas, at greater length.