Assalaamu alaykum respected scholars. My question is concerning the making up the raka'as inside the masjid and the location inside the masid to make up these raka'at that I miissed. I arrived late for salatul Asr just at the end of the second raka'as. at the end of the prayer and when the Imam gives 'As salaamu alaykum' I leave the line and move to the back of the masjid to make up the first two raka'at that I miss. One of the brothers told me afterwards that I cannot leave the line to make up the two raka'at, I must make up those raka't that I missed in the line and not alone in the back of the masjid. Another brother stated that since the Imam has concluded the salat, you are not obligated to stay in the line since those brothers who have completed the salat are leaving and you can make up those missed raka'at anywhere inside the masjid. please advise.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

You should have made up for the missed Rak`ahs in the same place where you prayed, rather than moving to the back of the Masjid. It was narrated that the Prophet performed prayer behind `Abdur-Rahmaan ibn `Awf and he missed one Rak`ah. When `Abdur-Rahmaan   made Tasleem, the Prophet made up for the missed Rak`ah without any addition and it was not reported that he moved from his place.

On the other hand, if the questioner gave his back to the Qiblah when he moved from his place, or walked many steps, then his prayer is invalid and he must repeat all of it because giving one’s back to the Qiblah in the obligatory prayer invalidates it, and much movement during prayer invalidates it as well.