Messenger of Allah ﷺ once led us in a prayer and offered two rakʿat and got up (for the third rakʿa) without sitting (after the second rakʿa). The people also got up with him, and when he was about to finish his prayer, we waited for him to finish the prayer with Taslim but he said Takbir before Taslim and performed two prostrations while sitting and then finished the prayer with Taslim. (Using translation from Bukhārī 1224)   

صَلَّى بِنَا رَسُولُ اللهِ ﷺ رَكْعَتَيْنِ مِنْ بَعْضِ الصَّلَوَاتِ ثُمَّ قَامَ فَلَمْ يَجْلِسْ فَقَامَ النَّاسُ مَعَهُ فَلَمَّا قَضَى صَلَاتَهُ وَنَظَرْنَا تَسْلِيمَهُ كَبَّرَ فَسَجَدَ سَجْدَتَيْنِ وَهُوَ جَالِسٌ قَبْلَ التَّسْلِيمِ ثُمَّ سَلَّمَ  

[Machine] That the Messenger of Allah ﷺ stood during two of the afternoon prayers without sitting in between. After completing his prayer, he prostrated twice and then gave the final salutation.  

أَنَّ رَسُولَ اللهِ ﷺ قَامَ فِي اثْنَتَيْنِ مِنَ الظُّهْرِ فَلَمْ يَجْلِسْ فِيهَا فَلَمَّا قَضَى صَلَاتَهُ سَجَدَ سَجْدَتَيْنِ ثُمَّ سَلَّمَ بَعْدَ ذَلِكَ  

[Machine] The Messenger of Allah ﷺ stood in the shaf' (middle) position, which he intended to sit in his prayer. He continued with his prayer, and when he reached the end of the prayer, he prostrated before giving the salutation (salam).  

أَنَّ رَسُولَ اللهِ ﷺ قَامَ فِي الشَّفْعِ الَّذِي يُرِيدُ أَنْ يَجْلِسَ فِي صَلَاتِهِ فَمَضَى فِي صَلَاتِهِ فَلَمَّا كَانَ فِي آخِرِ الصَّلَاةِ سَجَدَ قَبْلَ أَنْ يُسَلِّمَ ثُمَّ سَلَّمَ  

[Machine] I saw the Prophet ﷺ do that, and we have narrated from the hadith of Al-Mas'oodi from Ziyad bin 'Alaqa from Al-Mughirah bin Shu'bah something similar, and the Hadith of Ibn Buhaynah about prostration before the greeting is more authentic than that, and Allah knows best.  

رَأَيْتُ النَّبِيَّ ﷺ يَصْنَعُ ذَلِكَ وَقَدْ رُوِّينَا مِنْ حَدِيثِ الْمَسْعُودِيِّ عَنْ زِيَادِ بْنِ عِلَاقَةَ عَنِ الْمُغِيرَةِ بْنِ شُعْبَةَ مِثْلَهُ وَحَدِيثُ ابْنِ بُحَيْنَةَ فِي السُّجُودِ قَبْلَ السَّلَامِ أَصَحُّ مِنْ ذَلِكَ وَاللهُ أَعْلَمُ  

[Machine] When he finished, I performed as I had seen the Messenger of Allah ﷺ do and as narrated by Yahya ibn Yahya from Abu Mu'awiyah, and he added to it, then he prostrated for my two accidental prostrations. When he finished, he informed us that Abu Abdullah al-Hafiz informed Ibrahim ibn Isma'il ibn Ibrahim al-Adl, narrated by my father, narrated by Yahya ibn Yahya, who informed Abu Mu'awiyah, and he mentioned it in his meaning, and it was narrated specifically from Qais and he mentioned it to him on Sa'd.  

حِينَ انْصَرَفَ صَنَعْتُ كَمَا رَأَيْتُ رَسُولَ اللهِ ﷺ صَنَعَ وَرَوَاهُ يَحْيَى بْنُ يَحْيَى عَنْ أَبِي مُعَاوِيَةَ وَزَادَ فِيهِ ثُمَّ سَجَدَ سَجْدَتَيِ السَّهْوِ حِينَ انْصَرَفَ 3851 أَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ أنبأ إِبْرَاهِيمُ بْنُ عِصْمَةَ بْنِ إِبْرَاهِيمَ الْعَدْلُ ثنا أَبِي ثنا يَحْيَى بْنُ يَحْيَى أنبأ أَبُو مُعَاوِيَةَ فَذَكَرَهُ بِمَعْنَاهُ وَرَوَاهُ بَيَانٌ عَنْ قَيْسٍ فَوَقَفَهُ عَلَى سَعْدٍ  

[Machine] Subhan Allah, Subhan Allah. He did not sit and continued with his prayer. When he reached the end of his prayer, he made two prostrations of inadvertence while sitting. When he finished, he said, "I heard you saying 'Subhan Allah' before I sat down, but the sunnah that I have done and narrated to you is from a group of the Companions. Sufficient for us is what we have mentioned, and through Allah is our success."  

سُبْحَانَ اللهِ سُبْحَانَ اللهِ فَلَمْ يَجْلِسْ وَمَضَى عَلَى قِيَامِهِ فَلَمَّا كَانَ فِي آخِرِ صَلَاتِهِ سَجَدَ سَجْدَتَيِ السَّهْوِ وَهُوَ جَالِسٌ فَلَمَّا سَلَّمَ قَالَ إِنِّي سَمِعْتُكُمْ آنِفًا تَقُولُونَ سُبْحَانَ اللهِ لِكَيْمَا أَجْلِسَ لَكِنَّ السُّنَّةَ الَّذِي صَنَعْتُ وَرُوِّينَا ذَلِكَ عَنْ جَمَاعَةٍ مِنَ الصَّحَابَةِ ؓ وَفِيمَا ذَكَرْنَا كِفَايَةٌ وَبِاللهِ التَّوْفِيقُ