Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1261 (DarusSalam) ⓘ

It was narrated from Muhammad bin Yusuf, the freed slave of Uthman, from his father Yusuf, that: Mu'awiyah prayed in front of them, and he stood up during the prayer when he should have sat. The people said tasbih, but he remained standing, then he prostrated twice while he was sitting, after he completed the prayer. Then he sat on the Minbar and said: 'I heard the Messenger of Allah say: 'Whoever forgets something in his prayer, let him prostrate twice like this.'

أَخْبَرَنَا الرَّبِيعُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا شُعَيْبُ بْنُ اللَّيْثِ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ مُحَمَّدِ بْنِ عَجْلاَنَ، عَنْ مُحَمَّدِ بْنِ يُوسُفَ، مَوْلَى عُثْمَانَ عَنْ أَبِيهِ، يُوسُفَ أَنَّ مُعَاوِيَةَ، صَلَّى إِمَامَهُمْ فَقَامَ فِي الصَّلاَةِ وَعَلَيْهِ جُلُوسٌ فَسَبَّحَ النَّاسُ فَتَمَّ عَلَى قِيَامِهِ ثُمَّ سَجَدَ سَجْدَتَيْنِ وَهُوَ جَالِسٌ بَعْدَ أَنْ أَتَمَّ الصَّلاَةَ ثُمَّ قَعَدَ عَلَى الْمِنْبَرِ فَقَالَ إِنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏ "‏ مَنْ نَسِيَ شَيْئًا مِنْ صَلاَتِهِ فَلْيَسْجُدْ مِثْلَ هَاتَيْنِ السَّجْدَتَيْنِ ‏" ‏ ‏.‏