1744 كان رسول الله صلى الله عليه وسلم إذا انصرف من صلاته استغفر ثلاثا، وقال: اللهم أنت السلام ومنك السلام، تباركت يا ذا الجلال والإكرام
When the Messenger of Allah (may Allah's peace and blessings be upon him) finished his prayer, he would seek Allah’s forgiveness three times; then say: O Allah, You are the One free from imperfections, and peace and perfection come from You. Blessed are You, the Owner of Majesty and Honor

عن ثَوْبَان رضي الله عنه قال: كان رسول الله صلى الله عليه وسلم إذا انْصَرف من صلاته اسْتَغْفَر ثلاثا، وقال: «اللهُمَّ أنت السَّلام ومِنك السَّلام، تَبَارَكْتَ يا ذا الجَلال والإكْرَام».

Thawbān (may Allah be pleased with him) reported: When the Messenger of Allah (may Allah's peace and blessings be upon him) finished his prayer, he would seek Allah’s forgiveness three times; then say: "O Allah, You are the One free from imperfections, and peace and perfection come from You. Blessed are You, the Owner of Majesty and Honor."

صحيح - ( رواه مسلم ). Sahih/Authentic. [Muslim]

في الحديث بيان استحباب قول المصلي بعد الانتهاء من الصلاة: أستغفر الله، أستغفر الله، أستغفر الله. ثم يقول هذا الدعاء: اللَّهُمَّ أَنْتَ السَّلَامُ وَمِنْك السَّلَامُ، تَبَارَكْتَ يَا ذَا الْجَلَالِ وَالْإِكْرَامِ. وهناك أدعية أخرى وردت في أحاديث أخرى مما يقال عقب الصلاة.
The Hadīth indicates that it is recommended for a person offering the prayer to say after he finishes: “I seek Allah’s forgiveness" three times, then say the following supplication: “O Allah, You are the One free from imperfections, and peace and perfection come from You. Blessed are You, the Owner of Majesty and Honor." There are other supplications reported in other Hadīths to be said after finishing the prayer.

فيه الرَّد على من قال: أن المصلِّي يُكبر بعد الصلاة. فيه إثبات اسم: "السَّلام" لله -تعالى- وصفته، فهو السَّالم من كل نقص وعَيب، وهو واهب السَّلامة لعباده من شُرور الدُّنيا والآخرة.
It responds to those who say that one should say Takbīr (Allahu Akbar [Allah is Most Great]) after prayer. It establishes the name As-Salām for Allah Almighty, which means: The One free from all deficiencies and defects, and the Giver of safety to His ser