From Sahih Bukhari (Hadith 1025):
Narrated `Abbad bin Tamim from his uncle:"I saw the Prophet (ﷺ) on the day when he went out to offer the Istisqa' prayer. He turned his back towards the people and faced the Qibla and asked Allah for rain. Then he turned his cloak inside out and led us in a two rak`at prayer and recited the Qur'an aloud in them
Reference: Bukhari 1025