Musnad Ahmad 30:2806

'Abd al-Rahman narrated to us, he said: Shu'bah said: I heard Sa'id ibn Abi Sa'id al-Maqburi, after he had grown old, saying: I heard Abu Hurayrah saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Whatever is below the ankles of the lower garment is in the Fire."