Narrated Thauban (RA):

Whenever Allah's Messenger (ﷺ) finished his prayer, he used to say after asking Allah's forgiveness three times: "O Allah, You are as-Salam (One Free from every defect), and as-Salam (safety from every evil) is (sought) from You. Blessed are You, O Possessor of glory and honour." [Reported by Muslim].

وَعَنْ ثَوْبَانَ ‏- رضى الله عنه ‏- قَالَ : { كَانَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-إِذَا اِنْصَرَفَ مِنْ صَلَاتِهِ اِسْتَغْفَرَ اَللَّهَ ثَلَاثًا , وَقَالَ : " اَللَّهُمَّ أَنْتَ اَلسَّلَامُ وَمِنْكَ اَلسَّلَامُ .‏ تَبَارَكْتَ يَا ذَا اَلْجَلَالِ وَالْإِكْرَامِ } رَوَاهُ مُسْلِمٌ .‏ [1]‏