Musnad Abu Ya'la al-Mawsili 42:399

We used to go on military expeditions with the Messenger of Allah (may Allah bless him and grant him peace) during Ramadan. Among us were those who were fasting and those who were not fasting. The one who was fasting would not find fault with the one who was not fasting, nor would the one who was not fasting find fault with the one who was fasting. They held the view that whoever found strength and fasted, that was good, and they held the view that whoever found weakness and broke his fast, that was also good.