Sayyiduna Abu al-Darda' (may Allah be pleased with him) said: On some of the journeys with the Messenger of Allah (peace and blessings be upon him) we saw days that were extremely hot, so much so that one of us would place his hand on his head because of the intensity of the heat, and none of us was fasting except the Messenger of Allah (peace and blessings be upon him) and Sayyiduna Abdullah bin Rawahah (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8167