مختصر صحيح مسلم
Mukhtasar Sahih Muslim
Issues of Fasting
Choice to fast or not while traveling.
It is narrated from Sayyiduna Hamzah bin Amr Aslami (may Allah be pleased with him) that I asked, "O Messenger of Allah! I find myself strong enough to fast while traveling, so if I fast (during travel), is there any sin upon me?" The Prophet (peace and blessings of Allah be upon him) said, "It is a concession from Allah. So whoever takes it has done well, and whoever wishes to fast, there is no sin upon him."