ENOfficial
It was narrated from 'Imran bin Husain that: The Prophet (ﷺ) prayed three (rak'ahs) then said the taslim. Al-Khirbaq said: "You prayed three." So he led them in praying the remaining rak'ah, then he said the taslim, then he did the two prostrations of forgetfulness, then he said the taslim (again).
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا يَحْيَى بْنُ حَبِيبِ بْنِ عَرَبِيٍّ، قَالَ حَدَّثَنَا حَمَّادٌ، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَبِي الْمُهَلَّبِ، عَنْ عِمْرَانَ بْنِ حُصَيْنٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم صَلَّى ثَلاَثًا ثُمَّ سَلَّمَ فَقَالَ الْخِرْبَاقُ إِنَّكَ صَلَّيْتَ ثَلاَثًا . فَصَلَّى بِهِمُ الرَّكْعَةَ الْبَاقِيَةَ ثُمَّ سَلَّمَ ثُمَّ سَجَدَ سَجْدَتَىِ السَّهْوِ ثُمَّ سَلَّمَ .
sunnah.com