Sahih Bukhari Volume 008, Book 075, Hadith Number 403.

Narated 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."