Messenger of Allah ﷺ went out to this Musalla (praying place) to offer the prayer of Istisqa.' He invoked Allah for rain and then faced the Qibla and turned his Rida' (upper garment) inside out.  

خَرَجَ النَّبِيُّ ﷺ إِلَى هَذَا الْمُصَلَّى يَسْتَسْقِي فَدَعَا وَاسْتَسْقَى ثُمَّ اسْتَقْبَلَ الْقِبْلَةَ وَقَلَبَ رِدَاءَهُ