The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1948
Ibn Tamim narrated on the authority of his uncle ('Abdullah b. Zaid) that the Apostle of Allah (may peace be upon him) went out to the place of prayer and prayed for rain and faced towards Qibla, and turned round his mantle and prayed two rak'ahs.