We set out with the Messenger of Allah ﷺ during the month of Ramadan in intense heat, so much so that one of us would place his hand on his head from the severity of the heat. None of us was fasting except the Messenger of Allah ﷺ and Abdullah bin Rawahah.
خرجنا مع رسول الله ﷺ في شهر رمضان في حر شديد، حتى إن كان أحدنا ليضع يده على رأسه من شدة الحر وما فينا صائم إلا رسول الله ﷺ وعبد الله بن رواحة.
Bukhari in the Book of Fasting (1945), and Muslim in the Book of Fasting (1122), from the route of Ismail bin Ubaydullah, from Umm Darda, from Abu Darda, and he mentioned it. The wording is Muslim's. The wording of Bukhari is, "We went out with the Prophet ﷺ on one of his journeys on a hot day, so hot that a man would put his hand on his head from the intensity of the heat, and none of us was fasting except the Prophet ﷺ and Ibn Rawaha."