Hadith: The Prophet (may Allah’s peace and blessings be upon him) used to say after every obligatory prayer

عَنْ ‌وَرَّادٍ كَاتِبِ الْمُغِيرَةِ بْنِ شُعْبَةَ قَالَ: أَمْلَى عَلَيَّ الْمُغِيرَةُ بْنُ شُعْبَةَ فِي كِتَابٍ إِلَى مُعَاوِيَةَ:
أَنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ كَانَ يَقُولُ فِي دُبُرِ كُلِّ صَلَاةٍ مَكْتُوبَةٍ: «لَا إِلَهَ إِلَّا اللهُ وَحْدَهُ لَا شَرِيكَ لَهُ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ، وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ، اللَّهُمَّ لَا مَانِعَ لِمَا أَعْطَيْتَ، وَلَا مُعْطِيَ لِمَا مَنَعْتَ، وَلَا يَنْفَعُ ذَا الْجَدِّ مِنْكَ الْجَدُّ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 844]

Warrād, the scribe of Al-Mughīrah ibn Shu‘bah, related: Al-Mughīrah ibn Shu‘bah dictated to me in a letter to Mu‘āwiyah:
The Prophet (may Allah’s peace and blessings be upon him) used to say after every obligatory prayer: "Lā ilāh illa Allah, wahdahu lā sharīka lah, lahu al-mulku wa lahu al-hamdu wa huwa ‘ala koll shay’in qadīr, allahumma lā māni‘a lima a‘tayt wa lā mu‘tiya lima mana‘ta wa la banfa‘u dha al-jaddi minka al-jadd" (There is no god but Allah, alone, with no partner with Him. To Him belongs the dominion and to Him praise is due, and He is Able to do all things. O Allah, none can withhold what You give and none can give what You withhold, and riches cannot avail a wealthy person against You).
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 844]

Explanation

The Prophet (may Allah’s peace and blessings be upon him) used to say after every obligatory prayer: There is no god but Allah, alone, with no partner with Him. To Him belongs the dominion, and praise is due to Him, and He is Able to do all things. O Allah, none can withhold what You give, and none can give what You withhold, and riches cannot avail a wealthy person against You.
It means: I admit and acknowledge the phrase of Tawhīd (monotheism): There is no god but Allah. I affirm true worship for Allah and negate it from all else. No one is truly worthy of worship except Allah. I acknowledge that the true and complete dominion belongs to Allah, and the praise by all the inhabitants of the heavens and the earth is due to Allah Almighty, as He is Able to do all things, and what He predestined, of giving or withholding, cannot be prevented by anyone; and riches cannot avail a rich person with Him; rather it is the righteous deeds that avail him.