The Prophet ﷺ said: When an imam stands up at the end of two rak'ahs , if he remembers before standing straight up, he should sit down, but if he stands straight up, he must not sit down, but perform the two prostrations of forgetfulness. Abu Dawud said: I have not narrated in this book of mine any hadith from Jabir Al-Ju'fi (one of the narrators) except this one.  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا قَامَ الإِمَامُ فِي الرَّكْعَتَيْنِ فَإِنْ ذَكَرَ قَبْلَ أَنْ يَسْتَوِيَ قَائِمًا فَلْيَجْلِسْ فَإِنِ اسْتَوَى قَائِمًا فَلاَ يَجْلِسْ وَيَسْجُدُ سَجْدَتَىِ السَّهْوِ  

“The Messenger of Allah ﷺ said: ‘If anyone of you stands after two Rak’ah, if he has not yet stood up fully, let him sit down again, but if he has stood up fully, then let him not sit down, and let him perform two prostrations for forgetfulness (Sahw).’”  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا قَامَ أَحَدُكُمْ مِنَ الرَّكْعَتَيْنِ فَلَمْ يَسْتَتِمَّ قَائِمًا فَلْيَجْلِسْ فَإِذَا اسْتَتَمَّ قَائِمًا فَلاَ يَجْلِسْ وَيَسْجُدْ سَجْدَتَىِ السَّهْوِ  

“The Messenger of Allah ﷺ said: ‘If anyone of you stands after two Rak’ah, if he has not yet stood up fully, let him sit down again, but if he has stood up fully, then let him not sit down, and let him perform two prostrations for forgetfulness (Sahw).’” (Using translation from Ibn Mājah 1208)   

قَالَ رَسُولُ اللهِ ﷺ إِذَا قَامَ أَحَدُكُمْ فَلَمْ يَسْتَتِمَّ قَائِمًا فَلْيَجْلِسْ وَإِذَا اسْتَتَمَّ قَائِمًا فَلَا يَجْلِسْ وَيَسْجُدُ سَجْدَتَيِ السَّهْوِ  

The Prophet ﷺ said: When an imam stands up at the end of two rak'ahs , if he remembers before standing straight up, he should sit down, but if he stands straight up, he must not sit down, but perform the two prostrations of forgetfulness. Abu Dawud said: I have not narrated in this book of mine any hadith from Jabir Al-Ju'fi (one of the narrators) except this one. (Using translation from Abū Dāʾūd 1036)   

"إِذا قَام الإمامُ في الرَّكْعَتينْ فإِنْ ذكَر قبلَ أنْ يستوى قائِما فْليجِلسْ، فإنْ استوى قائما فلا يجْلسْ ويسجُدُ سجدتى السَّهو.