Sahih al-Bukhari 1026
Sahih al-Bukhari · Book 15: Invoking Allah for Rain (Istisqaa) · The Istisqa' prayer consists of two Rak'a
Narrated `Abbad bin Tamim from his uncle who said:
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ ، قَالَ حَدَّثَنَا سُفْيَانُ ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ ، عَنْ عَبَّادِ بْنِ تَمِيمٍ ، عَنْ عَمِّهِ ، أَنَّ النَّبِيَّ صلى الله عليه وسلم اسْتَسْقَى فَصَلَّى رَكْعَتَيْنِ، وَقَلَبَ رِدَاءَهُ.
"The Prophet (ﷺ) invoked Allah for rain and offered a two rak`at prayer and he put his cloak inside out."