The Book of Forgetfulness (In Prayer)
13/75. Chapter:
Prostration of forgetfulness after saying the salam and speaking
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ آدَمَ، عَنْ حَفْصٍ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم سَلَّمَ ثُمَّ تَكَلَّمَ ثُمَّ سَجَدَ سَجْدَتَىِ السَّهْوِ .
It was narrated from 'Abdullah that: The Prophet (ﷺ) said the salam, then he spoke, then he performed two prostrations of forgetfulness.
Reference : Sunan an-Nasa'i 1329In-book reference : Book 13, Hadith 151English translation : Vol. 2, Book 13, Hadith 1330