Sunan an Nasai
1262
Sahih+2

It was narrated that Abu Humaid As-Sa'idi said:"At the end of the last two rak'ahs of the prayer, the Prophet (ﷺ) would move his left foot forward and sit on his left buttock, Mutawarrikan, then he would say the taslim

SahihAbu Ghuddah
SahihAl-Albani