Sunan an-Nasa'i, Book 13, Hadith 151 (In-Book) ⓘ
It was narrated from 'Abdullah that: The Prophet said the salam, then he spoke, then he performed two prostrations of forgetfulness.
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 .
also referenced under: Hadith 1329 (Reference) & Volume 2, Book 13, Hadith 1330 (DarusSalam)