Sahih al-Bukhari 1031
Narrated Anas bin Malik:
The Prophet (ﷺ) never raised his hands for any invocation except for that of Istisqa' and he used to raise 
them so much that the whiteness of his armpits became visible. (Note: It may be that Anas did not see 
the Prophet (ﷺ) raising his hands, but it is narrated that the Prophet (ﷺ) used to raise his hands for invocations 
other than Istisqa. See Hadith No. 807 & 808 and also see Hadith No. 612, Vol. 5).
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا يَحْيَى، وَابْنُ أَبِي عَدِيٍّ، عَنْ سَعِيدٍ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم لاَ يَرْفَعُ يَدَيْهِ فِي شَىْءٍ مِنْ دُعَائِهِ إِلاَّ فِي الاِسْتِسْقَاءِ، وَإِنَّهُ يَرْفَعُ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ‏.‏