Sahih Bukhari
Invoking Allah for Rain (Istisqaa)
Volume: 002 / Book Number: 017 / Hadith Number: 137
Narrated Abbas bin Tamim from his uncle,
"I saw the Prophet on the day when he went out to offer the Istisqa' prayer. He turned his back towards the people and faced the Qibla and asked Allah for rain. Then he turned his cloak inside out and led us in a two Rakat prayer and recited the Qur'an aloud in them."