"The Messenger of Allah ﷺ said the salam then he performed two prostrations of forgetfulness while he was still sitting, then he said the salam." He said: He mentioned it in the hadith of Dhul-Yadain.
أَنَّ رَسُولَ اللَّهِ ﷺ سَلَّمَ ثُمَّ سَجَدَ سَجْدَتَىِ السَّهْوِ وَهُوَ جَالِسٌ ثُمَّ سَلَّمَ قَالَ ذَكَرَهُ فِي حَدِيثِ ذِي الْيَدَيْنِ