Sahih Muslim Book 4, Hadith Number 1950.

Chapter : Prayer for rain.

‘Abbad b. Tamim Mazini heard his uncle, who was one of the Companions of the Messenger of Allah (may peace be upon him), as saying: The Messenger of Allah (may peace be upon him) went out one day in order to pray for rain. He turned his back towards people, supplicated before Allah, facing towards Qibla, and turned his mantle round and then observed two rak’ahs of prayer.