(15) باب جواز الصوم والفطر في شهر رمضان للمسافر في غير معصية إذا كان سفره مرحلتين فأكثر وأن الأفضل لمن أطاقه بلا ضرر أن يصوم ولمن يشق عليه أن يفطر
Abu Khalid al-Ahmar narrated from Humaid who said:
I went out and was fasting; they said to me: Break (lit. go back, repeat). He said that Anas reported that the Companions of the Messenger of Allah (ﷺ) used to set out on a journey and neither the observer of the fast found fault with the breaker of the fast, nor the breaker of the fast found fault with the observer of the fast. (One of the narrators Humaid said): I met Ibn Abi Mulaika who informed me the same thing on the authority of 'A'isha.
Reference: Sahih Muslim 1118 b
In-book reference: Book 13, Hadith 127
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2483