Musnad Ahmad 30:1927

'Affan narrated to us, Wuhayb narrated to us, Suhayl narrated to us, from his father, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "For one of you to sit upon a burning coal, such that it burns his clothes until it reaches his skin, is better for him than to step upon the grave of a Muslim man."