What should a person do if he says the taslim following two rak'ahs by mistake and then
أَخْبَرَنَا مُحَمَّدُ بْنُ رَافِعٍ، قَالَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، قَالَ أَنْبَأَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، وَأَبِي، بَكْرِ بْنِ سُلَيْمَانَ بْنِ أَبِي حَثْمَةَ عَنْ أَبِي هُرَيْرَةَ، قَالَ صَلَّى رَسُولُ اللَّهِ صلى الله عليه وسلم الظُّهْرَ أَوِ الْعَصْرَ فَسَلَّمَ فِي رَكْعَتَيْنِ وَانْصَرَفَ . فَقَالَ لَهُ ذُو الشِّمَالَيْنِ بْنُ عَمْرٍو أَنُقِصَتِ الصَّلاَةُ أَمْ نَسِيتَ فَقَالَ النَّبِيُّ صلى الله عليه وسلم " مَا يَقُولُ ذُو الْيَدَيْنِ " . فَقَالُوا صَدَقَ يَا نَبِيَّ اللَّهِ . فَأَتَمَّ بِهِمُ الرَّكْعَتَيْنِ اللَّتَيْنِ نَقَصَ .
It was narrated that Abu Hurairah said: "The Messenger of Allah (ﷺ) prayed Zuhr or 'Asr and said the taslim following two rak'ahs and left. Dhul-Shimalain bin 'Amr said to him: 'Has the prayer been shortened or did you forget?" The Prophet (ﷺ) said: 'What is Dhul-Yadain saying?' They said: 'He is speaking the truth, O Messenger of Allah (ﷺ).' So he led them in praying the two rak'ahs that he missed."