Sahih Al Bukhari Hadith Number 1024

Narrated `Abbad bin Tamim: from his uncle who said, “The Prophet (peace be upon him) went out to invoke Allah for rain. He faced the Qibla invoking Allah. He turned over his cloak (inside out) and then offered two rak`at and recited the Qur’an aloud in them.”

15  Invoking Allah for Rain (Istisqaa)
Hadith number 1024
Volume no 2
Chapter: 16 (To recite aloud while offering the prayer of Istisqa’)