The World Federation One Stop Fiqh

Ruling 1263

With regard to someone who is certain that the journey he wants to go on is not eight farsakhs, or he doubts whether or not it is eight farsakhs, in the event that he realises on the way that his journey is eight farsakhs, he must perform qaṣr prayers even if only a short distance of his journey is left. If he has performed tamām prayers, he must perform them again in their shortened form; however, if the time has expired, it is not necessary for him to make them up.