Is it permissible to continue shortening prayers for a resident in a foreign country if he has not specified the duration of his stay, based on the fatwa of Sheikh Ibn Uthaymeen, knowing that he has been shortening prayers for a year and a half?

It is most probable that whoever intends to stay for four days or more should complete the prayer [i.e., not shorten it], and the days of arrival and departure are not counted within this period. The evidence for this is that Allah permitted shortening the prayer on the condition of travel, and one who is resident or intends to reside is not a traveler. They [the scholars] inferred the definition of residency as exceeding three nights from the Prophet’s (peace and blessings be upon him) saying: "The Muhajir may stay in Mecca for three [days] after completing his rituals."