Sahih Bukhari
Invoking Allah for Rain (Istisqaa)
Volume: 002 / Book Number: 017 / Hadith Number: 136
Narrated Abbas bin Tamim
from his uncle who said, "The Prophet went out to invoke Allah for rain. He faced the Qibla invoking Allah. He turned over his cloak (inside out) and then offered two Rakat and recited the Quran aloud in them."