I saw the Messenger of Allah (ﷺ) raising his hands (high enough) in supplication (for rain) that the whiteness of his armpits became visible.
Sahih Muslim Book 9, Hadith 5
← Previous Hadith The Messenger of Allah (ﷺ) went out one day in order to pray for rain. He turned his back towards people, supplicated before Allah, facing towards Qibla, and turned his mantle round and then observed two rak'ahs of prayer.

Sahih Muslim Book 9, Hadith 4 Next Hadith → Anas b. Malik reported that the Messenger of Allah (ﷺ) prayed for rain pointing the back of his hands to the sky.

Sahih Muslim Book 9, Hadith 6