Darul Uloom Trinidad & Tobago

Thauban (May Allah be pleased with him) reported:

When the Messenger of Allah (ﷺ) finished his prayer, he begged forgiveness from Allah three times and said: 

اللَّهُمَّ أَنْتَ السَّلاَمُ وَمِنْكَ السَّلاَمُ تَبَارَكْتَ يَا ذَا الْجِلَالِ وَالْإِكْرَامِ

Allahumma antas-salaam, wa minkas-salaam, tabarakta yaa dhal-Jalaali wal-‘Ikraam.

O Allah, You are Peace and from You comes peace. Blessed are You, O Owner of majesty and honor.

Walid reported: I said to Auza’i: How is the seeking of forgiveness? He replied: You should say: 

أَسْتَغْفِرُ اللَّهَ أَسْتَغْفِرُ اللَّهَ أَسْتَغْفِرُ اللَّهَ

Astaghfirullah! Astaghfirullah! Astaghfirullah!

I beg forgiveness from Allah, I beg forgiveness from Allah, I beg forgiveness from Allah.”

(Sahih Muslim, The Book of Mosques and Places of Prayer, Chapter: It is recommended to recite statements of remembrance after the prayer, and how that is to be done)