The Istisqa' prayer consists of two Rak'a
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.
Narrated `Abbad bin Tamim from his uncle who said: "The Prophet (ﷺ) invoked Allah for rain and offered a two rak`at prayer and he put his cloak inside out."