Sahih Bukhari, Chapter: Fasting

Ibn Abbas said, "Allah's Apostle set out from Medina to Makkah 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 Makkah, and that happened in Ramadan." Ibn Abbas used to say, "Allah's Apostle (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."