Prayer: If someone knowingly travels for sinful purposes, do they pray full or shortened?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: If someone knowingly travels for sinful purposes, do they pray full or shortened?

English:

Question #677:

If one knows that they will be engaged in sinful and ḥarām conduct during the journey they are about to make, will their prayer be full or shortened?

Answer #677:

If neither the journey nor its purpose is a sin but some harām practice is done during it, it is not ruled as a journey for sin and during it one should offer prayers in full form. Of course, if the sinful practice is done during the whole journey (except for few hours) so that the term “a journey for disobeying Allah” applies to it, it is a caution to offer the prayer in both full and shortened form.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer