The Messenger of Allah ﷺ performed the two prostrations of forgetfulness after the salam.
حدثنا حماد يعني ابن خالد حدثنا مالك عن داود يعني ابن الحصين عن أبي سفيان
سجد رسول الله ﷺ سجدتي السهو بعد السلام
Its isnad is sahih. Muslim narrated something similar to it in the Book of Mosques, 1/404, no. 573, Abu Dawud, 2/271, no. 1033, and Malik, 1/94.