Sunan Abi Dawud 1171
سنن أبي داود#1171SahihNarrated 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Muslim (896)
In-book reference: 3:11