We were traveling with the Prophet ﷺ, and some of us were fasting while others were not. We stopped to rest at a place on a hot day, and the one with the most shade among us was the one who had a cloak, while some of us were shielding ourselves from the sun with our hands.The fasting ones collapsed from exhaustion, while those who had broken their fast got up, pitched the tents, and watered the mounts. The Messenger of Allah ﷺ said, "Today those who broke their fast have taken away the reward."
كنا مع النبي ﷺ في السفر، فمنا الصائم ومنا المفطر، قال: فنزلنا منزلا في يوم حار، أكثرنا ظلا صاحب الكساء، ومنا من يتقي الشمس بيده. قال: فسقط الصوام، وقام المفطرون، فضربوا الأبنية وسقوا الركاب، فقال رسول الله ﷺ: ذهب المفطرون اليوم بالأجر.
Bukhari narrated it in jihad and expeditions (2890), and Muslim in fasting (1119), both through the route of Asim Ahwal, from Murawaq Ajli, from Anas, and he mentioned it. The wording given is Muslim's, while Bukhari's wording is abridged. In one of Muslim's versions it says, "So those who were not fasting girded themselves and worked," meaning they tied up their waists and worked on behalf of those who were fasting.