Musnad Ahmad 5:232

'Affan narrated to us, Hammad bin Salamah narrated to us, 'Ata' bin as-Sa'ib informed us, from Zadhan, that 'Ali bin Abi Talib said: I heard the Prophet, peace and blessings of Allah be upon him, saying: "Whoever leaves a place of a hair on his body from janabah (major ritual impurity) without water touching it, such and such will be done to him of the Fire." 'Ali said: "Therefore, I have declared enmity toward my hair, therefore I have declared enmity toward my hair."