If a person stands by the left side of the Imam, and the Imam dress him to the right from behind, the Salat (prayer) is correct.

Sahih al-Bukhari · Book 10 · Hadith 726

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا دَاوُدُ، عَنْ عَمْرِو بْنِ دِينَارٍ، عَنْ كُرَيْبٍ، مَوْلَى ابْنِ عَبَّاسٍ عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ صَلَّيْتُ مَعَ النَّبِيِّ صلى الله عليه وسلم ذَاتَ لَيْلَةٍ فَقُمْتُ عَنْ يَسَارِهِ، فَأَخَذَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِرَأْسِي مِنْ وَرَائِي، فَجَعَلَنِي عَنْ يَمِينِهِ، فَصَل…

Narrated Ibn `Abbas: I prayed with the Prophet (ﷺ) one night and stood on his left side. Allah's Messenger (ﷺ) caught hold of my head from behind and drew me to his right and then offered the prayer and slept. Later the…