Holding Fast to the Qur'an and Sunnah

Bukhari :: Book 9 :: Volume 92 :: Hadith 440

Narrated Anas:

The Prophet brought the Ansar and the Quarish people into alliance in my house at Medina, and he invoked Allah for one month against the tribe of Bani Sulaim in (the last Rak'a of each compulsory) prayer.