Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with this chain (it is narrated from Sayyiduna Abu Huraira, may Allah be pleased with him) that the Messenger of Allah, peace and blessings be upon him, said: "The fire of the children of Adam which you kindle is one part out of seventy parts of the fire of Hell." The people said: O Messenger of Allah! This fire alone would have been sufficient. He, peace and blessings be upon him, said: "The fire of Hell is sixty-nine degrees hotter than this."