It is narrated from Umayr, the freed slave of Abi al-Lahm (may Allah be pleased with him), that he said: I saw the Messenger of Allah (peace and blessings be upon him) at Ahjar al-Zayt praying for rain, with the inner sides of both his palms raised up.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14198