Sunnah After Salah

Thauban (May Allah be pleased with him) reported:
Whenever the Messenger of Allah (ﷺ) finished his Salat (prayer), he would beg forgiveness three times [by saying, ‘Astaghfirullah’ (3 times)] and then he would say: “Allahumma Antas-Salamu, wa minkas-Salamu, tabarakta ya Dhal-Jalali wal-Ikram. (O Allah! You are the Bestower of security and security comes from You; Blessed are You. O Possessor of glory and honour).”

[Muslim].Riyad as-Salihin
reference : Book 20, Hadith 8
Arabic/English book reference : Book 20, Hadith