Sahih Bukhari Volume 004, Book 053, Hadith Number 395.

Narated By 'Asim : I asked Anas about the Qunut (i.e. invocation in the prayer). Anas said, "It should be recited before bowing." I said, "So-and-so claims that you say that it should be recited after bowing." He replied, "He is mistaken." Then Anas narrated to us that the Prophet invoked evil on the tribe of Bani-Sulaim for one month after bowing. ' Anas Further said, "The Prophet had sent 40 or 70 Qaris (i.e. men well versed in the knowledge of the Qur'an) to some pagans, but the latter struggled with them and martyred them, although there was a peace pact between them and the Prophet I had never seen the Prophet so sorry and worried about anybody as he was about them (i.e. the Qaris)."