Musnad Abi Ya'la 1916 — he said: I used to pray the Zuhr prayer

It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) that he said: "I used to pray the Zuhr prayer with the Messenger of Allah (peace and blessings be upon him), and (because of the heat of the ground) I would take a handful of pebbles and hold them in my palms, then keep moving them from one palm to the other until they cooled, and then, because of the intensity of the heat, I would place them under my forehead in order to prostrate."