From Sahih Bukhari (Hadith 1948):
Narrated Tawus:Ibn `Abbas said, "Allah's Messenger (ﷺ) set out from Medina to Mecca and he fasted till he reached 'Usfan, where he asked for water and raised his hand to let the people see him, and then broke the fast, and did not fast after that till he reached Mecca, and that happened in Ramadan." Ibn `Abbas used to say, "Allah's Messenger (ﷺ) (sometimes) fasted and (sometimes) did not fast during the journeys so whoever wished to fast could fast, and whoever wished not to fast, could do so
Reference: Bukhari 1948