Narrated Thawban (RA):

The Prophet (ﷺ) said: "There are two prostrations after the Taslim (salutation) for each forgetfulness." [Abu Dawud and Ibn Majah reported it through a weak chain of narrators].

وَعَنْ ثَوْبَانَ ‏- رضى الله عنه ‏- أَنَّ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-قَالَ : { لِكُلِّ سَهْوٍ سَجْدَتَانِ بَعْدَمَا يُسَلِّمُ } رَوَاهُ أَبُو دَاوُدَ , وَابْنُ مَاجَهْ بِسَنَدٍ ضَعِيفٍ .‏ [1]‏