From Sahih Muslim (Hadith 2631):
Abu Darda' reported:We were with the Messenger of Allah (ﷺ) on some of his journeys on an intensely hot day so much so that a person would place his hand on his head (in order to protect himself) against excessive heat, and none amongst us was fasting but the Messenger of Allah (ﷺ) and Abdullah b. Rawaha
Reference: Muslim 2631