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 ﷺ say: 'Whoever forgets something in his prayer, let him prostrate twice like this.' (Using translation from Nasāʾī 1260)  

أَنَّ مُعَاوِيَةَ صَلَّى أَمَامَهُمْ فَقَامَ فِي الصَّلَاةِ وَعَلَيْهِ جُلُوسٌ فَسَبِّحَ النَّاسُ فَتَمَّ عَلَى قِيَامِهِ ثُمَّ سَجَدَ بِنَا سَجْدَتَيْنِ وَهُوَ جَالِسٌ بَعْدَ أَنْ أَتَمَّ الصَّلَاةَ ثُمَّ قَعَدَ عَلَى الْمِنْبَرِ فَقَالَ إِنِّي سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ «مَنْ نَسِيَ مِنْ صَلَاتِهِ شَيْئًا فَلْيَسْجُدْ مِثْلَ هَاتَيْنِ السَّجْدَتَيْنِ»