Shortening is the established Sunnah of the Prophet (ﷺ) for every traveller, from the moment he leaves the buildings of his town until he returns to them — even if his journey is short. He (ﷺ) did not specify a fixed distance, and the reports of the Companions show variation; what is established is that any journey known by the people as "safar" is sufficient. He may shorten as long as he has not formed a settled intention to reside (over four days according to the most authentic position); if he intends a stay of more than four days he prays in full. Shortening is more beloved to Allah than completing while travelling, for it is His charity to His slaves.