Anas reported that the Messenger of Allah ﷺ was not accustomed to raice his hands in any supplication he made except when praying for rain. (He would then raise [his hands] high enough) that the whiteness of his armpits became visible. 'Abd al-A'la said that (he was in doubt whether it was) the whiteness of his armpit or armpits.
أَنَّ نَبِيَّ اللَّهِ ﷺ كَانَ لاَ يَرْفَعُ يَدَيْهِ فِي شَىْءٍ مِنْ دُعَائِهِ إِلاَّ فِي الاِسْتِسْقَاءِ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ غَيْرَ أَنَّ عَبْدَ الأَعْلَى قَالَ يُرَى بَيَاضُ إِبْطِهِ أَوْ بَيَاضُ إِبْطَيْهِ