He saw the Messenger of Allah ﷺ, when he prayed for rain, turn to face the Qiblah, turning his cloak around and raising his hands. (Using translation from Nasāʾī 1512)  

أَنَّهُ رَأَى رَسُولَ اللهِ ﷺ «فِي الِاسْتِسْقَاءِ اسْتَقْبَلَ الْقِبْلَةَ وَقَلَبَ الرِّدَاءَ وَرَفَعَ يَدَيْهِ»  

The Prophet (peace be upon him) was not accustomed to raise his hands in any supplication he made except when praying for rain. He would then raise them high enough so much so that the whiteness of his armpits was visible. (Using translation from Abū Dāʾūd 1170)  

كَانَ رَسُولُ اللهِ ﷺ «لَا يَرْفَعُ يَدَيْهِ فِي شَيْءٍ مِنَ الدُّعَاءِ إِلَّا فِي الِاسْتِسْقَاءِ فَإِنَّهُ كَانَ يَرْفَعُ يَدَيْهِ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ»