Musannaf Ibn Abi Shaybah 39348 — The acceptance of Islam by Abu Bakr

Al-Sha'bi said: Except for Sayyiduna Khabbab (may Allah be pleased with him), the rest gave them what they demanded. So the polytheists pressed the back of Sayyiduna Khabbab onto heated stones until the moisture of his back was gone. (Perhaps the melting of the fat of his back is meant.)