Would Fire Consume the Marks of Postration?
Abu Hurairah reported: "The Messenger of Allah said: "There will be a bridge laid across Hell." And I will be the first to pass over it. The only invocation that the Messengers then would say is: "O Allah safeguards us". "It is a slippery (bridge) on which there are clamps and (hooks like) thorns that scratch people according to their deeds, some will be totally safe, and some will be safe after receiving some scratches, and some will fall down into Hell (fire). After Allah, Exalted is He, finishs judging His slaves, He takes out from Hell some of those who beared witnessed that there is deity worthy of worship but Allah, so He orders His angels to bring them out. When angels took for them, they recognise then by the marks of postration. Because Allah, the Most High, forbade fire to consume the marks of postration. They take them out, thought their bodies were burnt, so they pour on them water, called the water of life. They will grow on its banks, as a seed carried by the torrent grow."
Ahmad in his Musnad (2/275-276), Sahih al-Bukhari (1/204) and Sahih Muslim (182)