Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) said: Together with the Prophet (peace and blessings be upon him) we visited a man who was suffering (with fever). He said: I placed my hand on him and said: "By Allah!" I have never seen a man as hot as this. The Prophet (peace and blessings be upon him) said: "Shall I not tell you of those who will be hotter than him on the Day of Resurrection? These two men who are turning away and leaving," and he pointed to two men who were at that time among his companions.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16835