Sahih al-Bukhari, Hadith 3565 ⓘ

Narrated Anas: Allah's Messenger did not use to raise his hands in his invocations except in the Istisqa (i.e. invoking Allah for the rain) in which he used to raise his hands so high that one could see the whiteness of his armpits. (Note: It may be that Anas did not see the prophet (as) raising his hands but it has been narrated that the Prophet (as) used to raise his hands for invocations other than Istisqa. See Hadith No. 612 Vol. 5. and Hadith No. 807 & 808 Vol 2.)

حَدَّثَنَا عَبْدُ الأَعْلَى بْنُ حَمَّادٍ، حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، أَنَّ أَنَسًا ـ رضى الله عنه ـ حَدَّثَهُمْ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ لاَ يَرْفَعُ يَدَيْهِ فِي شَىْءٍ مِنْ دُعَائِهِ، إِلاَّ فِي الاِسْتِسْقَاءِ، فَإِنَّهُ كَانَ يَرْفَعُ يَدَيْهِ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ‏.‏ وَقَالَ أَبُو مُوسَى دَعَا النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَرَفَعَ يَدَيْهِ وَرَأَيْتُ بَيَاضَ إِبْطَيْهِ