Hadith 1412
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) made the supplication for rain (du'a al-istisqa) in such a way that he spread out both his hands, and their palms were facing towards the ground, until I saw the whiteness of his armpits.
Hadith 1413
Abu Hurairah (may Allah be pleased with him) narrates that I saw the Messenger of Allah (peace be upon him) spreading his hands (so much) that I saw the whiteness of his armpits. In the narration of Sulaiman, these words are present: I think that the Prophet (peace be upon him) was supplicating for rain (Istisqa).