I said to Mujahid, "What about fasting while traveling?"He replied, "The Messenger of Allah ﷺ would sometimes fast and sometimes break his fast."
أخبرنا حميد بن مسعدة قال حدثنا سفيان
قلت لمجاهد الصوم في السفر قال كان رسول الله ﷺ يصوم ويفطر
No references are available.
[Sahih] See the previous and following hadith. It is in Kubra, hadith no. 2600.