Sahih Al Bukhari (482)

عن حميد عن أنس بن مالك {أن النبي صلى الله عليه وسلم كان إذا غزا بنا قوما لم يكن يغزو بنا حتى يصبح وينظر فإن سمع أذانا كف عنهم وإن لم يسمع أذانا أغار عليهم قال فخرجنا إلى خيبر فانتهينا إليهم ليلا فلما أصبح ولم يسمع أذانا ركب وركبت خلف أبي طلحة وإن قدمي لتمس قدم النبي صلى الله عليه وسلم قال فخرجوا إلينا بمكاتلهم ومساحيهم فلما رأوا النبي صلى الله عليه وسلم قالوا محمد والله محمد والخميس قال فلما رآهم رسول الله صلى الله عليه وسلم قال الله أكبر الله أكبر خربت خيبر إنا إذا نزلنا بساحة قوم {فساء صباح المنذرين}

Humayd reported: Anas ibn Malik said, “Whenever the Prophet (peace be upon him) went out with us to fight (in Allah’s cause) against any nation, he never allowed us to attack till morning and he would wait and see: if he heard Adhan he would postpone the attack and if he did not hear Adhan he would attack them.” Anas added, “We reached Khaybar at night and in the morning when he did not hear the Adhan for the prayer, he (the Prophet (peace be upon him)) rode and I rode behind Abu Talhah and my foot was touching that of the Prophet (peace be upon him). The inhabitants of Khaybar came out with their baskets and spades and when they saw the Prophet (peace be upon him) they shouted ‘Muhammad! By Allah, Muhammad and his army.’ When Allah’s Messenger (peace be upon him) saw them, he said, “Allahu-Akbar! Allahu-Akbar! Khaybar is ruined. Whenever we approach a (hostile) nation (to fight), then evil will be the morning of those who have been warned.”