Question: For which type of journey is not having to fast permissible?
Answer: The journey for which it is permissible to shorten the prayer and not fast is approximately 83 kilometres. There are some amongst the scholars who do not specify a distance for the journey, rather, all that is commonly understood as a journey amongst the people constitutes a journey. The Messenger of Allah (peace be upon him) used to shorten the prayer if he travelled 3 farasikh (plural of farsakh, i.e. 3 miles - which is equal to 9 miles). And for the impermissible journey, it is not acceptable to shorten the prayer or not to fast because a journey (undertaken) for (any) evil acts is not appropriate for (such a) permissibility. However, some of the people of knowledge do not differentiate between a journey (undertaken) for (any) evil acts or a journey in obedience (to Allah) for the generality of the evidence (available).
And (ultimately) the (complete) knowledge is with Allah.