We used to go on military expeditions with the Messenger of Allah ﷺ, and among us were those who fasted and those who did not. The one fasting found no fault with the one not fasting, nor did the one not fasting find fault with the one fasting. They held that whoever felt strong enough to fast, it was good for him to do so, and whoever felt weak and broke his fast, that too was good.
حدثنا إسماعيل أخبرنا الجريري عن أبي نضرة
كنا نغزو مع رسول الله ﷺ فمنا الصائم ومنا المفطر فلا يجد الصائم على المفطر ولا المفطر على الصائم يرون أنه يعني من وجد قوة فصام فإن ذلك حسن ويرون أنه من وجد ضعفا فأفطر فإن ذلك حسن
Its isnad is sahih. Jareeri is Saeed bin Iyas mentioned previously. The hadith is found in Muslim 2/787, no. 1115, in the Book of Fasting, on the permissibility of fasting or breaking the fast while traveling, and in Tirmidhi 3/83, no. 713, where he said, hasan sahih.