(3) باب رَفْعِ الْيَدَيْنِ فِي الاِسْتِسْقَاءِ
Narrated Anas:
The Prophet (ﷺ) used to make supplication for rain in this manner. he spread his hands keeping the inner side (of hands) towards the earth, so I witnessed the whiteness of his armpits.
Reference: Sunan Abi Dawud 1171
In-book reference: Book 3, Hadith 11
English translation: Book 3, Hadith 1167