Invoking Allah for Rain (Istisqaa)

Bukhari :: Book 2 :: Volume 17 :: Hadith 135

Narrated Abbas bin Tamim

that his uncle (who was one of the companions of the Prophet) had told him, "The Prophet went out with the people to invoke Allah for rain for them. He stood up and invoked Allah for rain, then faced the Qibla and turned his cloak (inside out) and it rained."