Narrated Anas bin Malik:

Allah's Apostle reached Khaibar in the early morning and the people of Khaibar came out with their spades, and when they saw the Prophet they said, "Muhammad and his army!" and returned hurriedly to take refuge in the fort. The Prophet raised his hands and said, "Allah is Greater! Khaibar is ruined ! If we approach a nation, then miserable is the morning of those who are warned."

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا أَيُّوبُ، عَنْ مُحَمَّدٍ، سَمِعْتُ أَنَسَ بْنَ مَالِكٍ ـ رضى الله عنه ـ يَقُولُ صَبَّحَ رَسُولُ اللَّهِ ﷺ خَيْبَرَ بُكْرَةً وَقَدْ خَرَجُوا بِالْمَسَاحِي، فَلَمَّا رَأَوْهُ قَالُوا مُحَمَّدٌ وَالْخَمِيسُ. وَأَحَالُوا إِلَى الْحِصْنِ يَسْعَوْنَ، فَرَفَعَ النَّبِيُّ ﷺ يَدَيْهِ وَقَالَ
" اللَّهُ أَكْبَرُ، خَرِبَتْ خَيْبَرُ، إِنَّا إِذَا نَزَلْنَا بِسَاحَةِ قَوْمٍ فَسَاءَ صَبَاحُ الْمُنْذَرِينَ ".