The Albaani Site

Questioner: The ruling about someone who prays alone behind a row?

Al-Albaani: If he prays behind the row [out of necessity] then he is excused and does not have to repeat the prayer, but if he prays behind it out of carelessness in implementing the legislation—which is to join the row in front of him when he is able to—but didn’t, then in this case his prayer is invalid and he has to repeat it.

Al-Hudaa wan-Noor, 90.