Sunan an-Nasai 16254
In-book no 1518أَخْبَرَنِي شُعَيْبُ بْنُ يُوسُفَ، عَنْ يَحْيَى بْنِ سَعِيدٍ الْقَطَّانِ، عَنْ سَعِيدٍ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم لاَ يَرْفَعُ يَدَيْهِ فِي شَىْءٍ مِنَ الدُّعَاءِ إِلاَّ فِي الاِسْتِسْقَاءِ فَإِنَّهُ كَانَ يَرْفَعُ يَدَيْهِ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ .
It was narrated that Anas said: "The Messenger of Allah (ﷺ) did not raise his hands during any supplication except when praying for rain, when he used to raise his hands so high that the whiteness of his armpits could be seen."