كتاب الصلاة
2  
The Book of Prayer
Bulugh al-Maram 339
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
Reference : Bulugh al-Maram 339
In-book reference : Book 2, Hadith 339
English translation : Book 2, Hadith 334
Hadith Text
Reference