It was narrated from 'Abdur-Rahman Al A'raj that:Abdullah bin Buhainah told him that the Messenger of Allah (ﷺ) stood up following two rak'ahs of Zuhr and did not sit down (for tashahhud). When he finished the prayer he prostrated twice, saying Takbir for each prostration, while he was sitting, before he said the taslim, and the people prostrated with him. (He did that) in place of the sitting that he had forgotten.
أَخْبَرَنَا أَحْمَدُ بْنُ عَمْرِو بْنِ السَّرْحِ، قَالَ أَنْبَأَنَا ابْنُ وَهْبٍ، قَالَ أَخْبَرَنِي عَمْرٌو، وَيُونُسُ، وَاللَّيْثُ، أَنَّ ابْنَ شِهَابٍ، أَخْبَرَهُمْ عَنْ عَبْدِ الرَّحْمَنِ الأَعْرَجِ، أَنَّ عَبْدَ اللَّهِ ابْنَ بُحَيْنَةَ، حَدَّثَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَامَ فِي الثِّنْتَيْنِ مِنَ الظُّهْرِ فَلَمْ يَجْلِسْ فَلَمَّا قَضَى صَلاَتَهُ سَجَدَ سَجْدَتَيْنِ كَبَّرَ فِي كُلِّ سَجْدَةٍ وَهُوَ جَالِسٌ قَبْلَ أَنْ يُسَلِّمَ وَسَجَدَهُمَا النَّاسُ مَعَهُ مَكَانَ مَا نَسِيَ مِنَ الْجُلُوسِ .
Nesai
The Book of Forgetfulness (In Prayer) • Hadith 1261