Hadith: Allahumma anta as-salām wa minka as-salām, tabārakta yadha al-jalāl wa al-ikrām

عن ثَوْبَانَ رضي الله عنه قال:
كَانَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ إِذَا انْصَرَفَ مِنْ صَلَاتِهِ اسْتَغْفَرَ ثَلَاثًا، وَقَالَ: «اللَّهُمَّ أَنْتَ السَّلَامُ، وَمِنْكَ السَّلَامُ، تَبَارَكْتَ ذَا الْجَلَالِ وَالْإِكْرَامِ»، قَالَ الْوَلِيدُ: فَقُلْتُ لِلْأَوْزَاعِيِّ: كَيْفَ الْاسْتِغْفَارُ؟ قَالَ: تَقُولُ: أَسْتَغْفِرُ اللهَ، أَسْتَغْفِرُ اللهَ.
[صحيح] - [رواه مسلم] - [صحيح مسلم: 591]

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 and say: "Allahumma anta as-salām wa minka as-salām, tabārakta yadha al-jalāl wa al-ikrām (O Allah, You are As-Salām (peace, perfection), and as-salām comes from You. Blessed are You, O Possessor of Glory and Honor)". Al-Walīd said: I said to Al-Awzā‘i: "How is the seeking of forgiveness?" He said: "You say: Astaghfirullāh, astaghfirullāh (I seek forgiveness from Allah, I seek forgiveness from Allah)."
[Authentic hadith] - [Narrated by Muslim] - [Sahih Muslim - 591]

Explanation

When the Prophet (may Allah's peace and blessings be upon him) finished his prayer, he would say: I seek forgiveness from Allah, I seek forgiveness from Allah, I seek forgiveness from Allah.
Then, he would glorify his Lord, saying: "O Allah, You are As-Salām (peace, perfection), and as-salām comes from You. Blessed are You, O Possessor of Glory and Honor." Indeed, Allah is complete and perfect in His attributes and far exalted above any imperfection or defect. From Him alone, and not from others, we should ask for safety from the evils of this world and the Hereafter. He, Exalted be He, gives abundant blessings in both abodes, and He is the Possessor of greatness and benevolence.