Thawban reported,

When the Messenger of Allah ﷺ finished his prayer, he would seek Allah's forgiveness three times, then say, "O Allah, You are Peace, and from You comes peace. Blessed are You, Possessor of Majesty and Honor."Walid said, I asked Awzai, "How is the seeking of forgiveness done?"He replied, "You say, 'I seek Allah's forgiveness, I seek Allah's forgiveness.'"

Azami 13475

Sahih

عن ثوبان قال

كان رسول الله ﷺ إذا انصرف من صلاته، استغفر الله ثلاثا، وقال: اللهم أنت السلام، ومنك السلام، تباركت ذا الجلال والإكرام. قال الوليد: فقلت للأوزاعي: كيف الاستغفار؟ قال: تقول: أستغفر الله، أستغفر الله.

الأعظمي 13475صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Tafsir of the great Quran
Chapter
Tafsir of Surah Rahman
Section
His saying, "Blessed is the name of your Lord, Owner of majesty and honor"
Numbering
Jami al-Kamil 13475 (2nd edition)
Azami 13475