What is the ruling on the prayer of one who intended to travel for four days, and on the fifth day to another city, so he performed the prayers in full and shortened them, then the trip on the fifth day was canceled and he remained in the first city, so he continued to combine and shorten the prayers?

There is no harm in utilizing the travel concessions for the period mentioned in the question, due to the absence of an intention to reside for four full days, excluding the days of arrival and departure. Remaining longer than that due to an excuse does not cause harm, because staying does not interrupt the journey as long as the intention to reside has not been formed. The proof for this is that whoever enters a country with the intention of leaving tomorrow or the day after, and does not intend a period of stay, may shorten their prayers even if they remain for years. And whoever does not intend to reside for a period exceeding twenty-one prayers may shorten their prayers, even if they stay for years, such as someone who stays to fulfill a need hoping for its success.