Hadith 141
Sayyiduna Ali (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) said: "Whoever, during the ritual bath of major impurity, leaves even a single hair on his body unwashed, such and such will be done to him in Hell." Sayyiduna Ali (may Allah be pleased with him) says: That is why I became an enemy of the hair of the head. And he used to cut his hair.