Yahya related to me from Malik from Nafi that Abdullah ibn Umarused to place his palms flat on the surface where he put his forehead.Nafi said, "I have seen him take his hands out from under his burnuson a very cold day and place them on the ground."
USC-MSA web (English) reference: Book 9, Hadith 62
Arabic reference: Book 9, Hadith 393