What should a traveler do if, during their journey, they become certain of their return date? Should they immediately cease shortening prayers, or should they shorten prayers for an additional four days and then pray in full, especially if their madhhab necessitates completing the prayer after four days of a known travel duration?

The madhhab (school of thought) of the majority of scholars is that if one intends to stay in a country for more than four days, he must complete the four-rak'ah prayers and not shorten them. The ruling of travel ceases for him from the moment of this intention. It is a clear error for him to shorten for four days and then complete afterward.

As for someone who does not intend a specific duration of stay and says, "I'll leave today, I'll leave tomorrow," and the fulfillment of his need is likely within a short period, he may shorten his prayers even if he stays for years.

Therefore, if you intend to stay on your journey for more than four days, you are obligated to complete your prayers from the moment of your intention; otherwise, you may shorten them.

The four-rak'ah prayers that you shortened when shortening was not permissible are considered a debt upon you, and you must make them up, for the Prophet, peace and blessings be upon him, said: "The debt owed to Allah is more deserving of being fulfilled."