Musnad Ahmad 1151:1

Hassan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, Muhammad ibn Zayd ibn al-Muhajir ibn Qunfudh narrated to us, from Umayr, the freed slave of Abi al-Lahm, who said: I saw the Messenger of Allah, may Allah bless him and grant him peace, at the Stones of Oil (Ahjar al-Zayt) seeking rain, raising the palms of his hands.