Musnad Ahmad 31:805

Yunus narrated to us, Hammad—meaning Ibn Salamah—narrated to us, from Bishr ibn Harb, who said: I heard Abu Sa’id say: "The Messenger of Allah (peace and blessings of Allah be upon him) stood at Arafah, and he began to supplicate like this, and he placed the backs of his palms toward his face, and he raised them above his chest and below his shoulders."