Musannaf Ibn Abi Shayba 3:392

Abu Bakr narrated to us, he said: Bishr bin al-Mufaddal narrated to us, from Ghalib, from Bakr, from Anas, who said: We used to pray with the Prophet, may Allah bless him and grant him peace, in the intense heat. If one of us could not place his face firmly upon the ground, he would spread his garment and prostrate upon it.