Sahih Al Bukhari Hadith Number 1012

Narrated `Abdullah bin Zaid: The Prophet (peace be upon him) went towards the Musalla and invoked Allah for rain. He faced the Qibla and wore his cloak inside out, and offered two rak`at.

15  Invoking Allah for Rain (Istisqaa)
Hadith number 1012
Volume no 2
Chapter: 4 ( Turning cloak inside out while offering the Istisqa’ prayer)