Sahih Bukhari Volume 8, Book 80, Hadith 6396

حَدَّثَنَا الْحَسَنُ بْنُ الرَّبِيعِ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ عَاصِمٍ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ بَعَثَ النَّبِيُّ صلى الله عليه وسلم سَرِيَّةً يُقَالُ لَهُمُ الْقُرَّاءُ فَأُصِيبُوا، فَمَا رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم وَجَدَ عَلَى شَىْءٍ مَا وَجَدَ عَلَيْهِمْ، فَقَنَتَ شَهْرًا فِي صَلاَةِ الْفَجْرِ وَيَقُولُ ‏"‏ إِنَّ عُصَيَّةَ عَصَوُا اللَّهَ وَرَسُولَهُ ‏"‏‏

Narrated By Anas : The Prophet sent a Sariya (an army detachment) consisting of men called Al-Qurra', and all of them were martyred. I had never seen the Prophet so sad over anything as he was over them. So he said Qunut (invocation in the prayer) for one month in the Fajr prayer, invoking for Allah's wrath upon the tribe of 'Usaiya, and he used to say, "The people of 'Usaiya have disobeyed Allah and His Apostle."