What is the ruling on making up a missed prayer while one is traveling?

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If a traveler forgets a prayer and remembers it while still traveling, the missed prayer must be performed in the shortened (qasr) form. This is because the prayer became obligatory and was performed during travel, resembling the case where it is performed at its appointed time. This ruling applies even if the traveler remembers it during a subsequent journey or whether they remember it while traveling or residing. The basis for this ruling is that the obligation and performance occurred during travel, thus maintaining the character of a traveler's prayer, even if remembered later.