Hamza al-Aslami asked the Messenger of Allah ﷺ about fasting while traveling, as he was a man who fasted continuously. He replied, "If you wish, fast, and if you wish, break your fast."
أخبرنا إسحق بن إبراهيم قال أنبأنا عبدة بن سليمان قال حدثنا هشام بن عروة عن أبيه
أن حمزة الأسلمي سأل رسول الله ﷺ عن الصوم في السفر وكان رجلا يسرد الصيام فقال إن شئت فصم وإن شئت فأفطر
[Sahih] See the two preceding hadiths. It is also found in Kubra, no. 2616. Tirmidhi also narrated it in the Book of Fasting, in the chapter on the concession regarding fasting while traveling, no. 711, from the hadith of Abdah, with the same wording, and he said, hasan sahih.