The Imaam said, “And the scholars have differed about fasting while on a journey in Ramadaan, there being a number of opinions, and there is no doubt that not fasting during a journey is allowed, and doing that is the preferred option in our opinion if the person not keeping it doesn’t find it difficult to make it up [later], otherwise [i.e., if he does find it difficult to make up later] we prefer that he fasts, and Allaah knows best. And whoever wants to delve further into this topic should refer to Nailul-Awtaar or other books of the people of knowledge.”
Ad-Da’eefah, vol. 2, pp. 336-337.
Commenting on al-Mundhiri’s statement on whether or not to fast when on a journey, the Imaam said, “And he, may Allaah have mercy on him, spoke the truth [when he said], ‘And the better of the two options is the one that is easier.’ People’s strength and circumstances differ, let each one do what is easier for him, and that is why it has been authentically reported that the Prophet صلى الله عليه وسلم, when asked about fasting on a journey, said, ‘Fast if you want, or break it if you want.’ (Reported by Muslim 3/145). And from another authentic path [of narration] with the wording, ‘Whichever is easier for you, do it,’ and it has been checked in As-Saheehah, 2884.”
At-Ta’leeq alat-Targheeb wat-Tarheeb, 1/456.