Prayer: Realising a Journey Was Not Eight Farsakhs After Performing Qaṣr Prayers
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1262
If someone who is certain that his journey is eight farsakhs performs qaṣr prayers and later realises that it was not eight farsakhs, he must perform them as four rakʿah prayers; and if the time has expired, he must make them up.