Invoking Allah for Rain (Istisqaa)
15/21. Chapter:
While offering the Istisqa' prayer, people should raise hands along with the Imam
Sahih Bukhari
وَقَالَ الأُوَيْسِيُّ حَدَّثَنِي مُحَمَّدُ بْنُ جَعْفَرٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، وَشَرِيكٍ، سَمِعَا أَنَسًا، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ رَفَعَ يَدَيْهِ حَتَّى رَأَيْتُ بَيَاضَ إِبْطَيْهِ.
The narrator Anas added that the Prophet (ﷺ) raised his hands (during the invocation) to such an extent that the whiteness of his armpits was visible.
Reference : Sahih al-Bukhari 1030In-book reference : Book 15, Hadith 25USC-MSA web (English) reference : Vol. 2, Book 17, Hadith 140