Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) used to celebrate Allah’s oneness with these words after every prayer

عَنْ ‌أَبِي الزُّبَيْرِ قَالَ:
كَانَ ‌ابْنُ الزُّبَيْرِ يَقُولُ فِي دُبُرِ كُلِّ صَلَاةٍ حِينَ يُسَلِّمُ: «لَا إِلَهَ إِلَّا اللهُ وَحْدَهُ لَا شَرِيكَ لَهُ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ، لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللهِ، لَا إِلَهَ إِلَّا اللهُ، ‌وَلَا ‌نَعْبُدُ ‌إِلَّا إِيَّاهُ، لَهُ النِّعْمَةُ وَلَهُ الْفَضْلُ وَلَهُ الثَّنَاءُ الْحَسَنُ، لَا إِلَهَ إِلَّا اللهُ مُخْلِصِينَ لَهُ الدِّينَ وَلَوْ كَرِهَ الْكَافِرُونَ» وَقَالَ: «كَانَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يُهَلِّلُ بِهِنَّ دُبُرَ كُلِّ صَلَاةٍ».
[صحيح] - [رواه مسلم] - [صحيح مسلم: 594]

Abu az-Zubayr reported:
Ibn az-Zubayr (may Allah be pleased with him) used to say after every prayer after making taslīm: “Lā ilāha illa Allah wahdahu lā sharīka lahu, lahu al-mulk wa lahu al-hamd wa huwa ‘ala kolli shay‘in qadīr; lā hawla wa lā quwwata illa billāh, lā ilāha illa Allah, wa lā na‘budu illa iyyāh, lahu an-ni‘mah wa al-fadl, wa lahu ath-thanā’ al-hasan; lā ilāha illa Allah, mukhlisīn lahu ad-dīn wa law kariha al-kāfirūn (There is no god but Allah, alone, with no partner. To Him belongs the dominion, and praise is due to Him, and He has power over all things. There is no power or strength except through Allah. There is no god but Allah, and we worship none but Him. To Him belongs the blessing, to Him belongs the grace, and to Him belongs all excellent praise. There is no god but Allah; we are sincerely devoted to Him, even if the disbelievers may dislike it)." And he said: "The Messenger of Allah (may Allah's peace and blessings be upon him) used to celebrate Allah’s oneness with these words after every prayer."
[Authentic hadith] - [Narrated by Muslim] - [Sahih Muslim - 594]

Explanation

The Messenger of Allah (may Allah's peace and blessings be upon him) used to celebrate Allah's oneness after making taslīm at the end of every obligatory prayer with this great dhikr, which means:
"There is no god but Allah" means: None is truly worthy of worship except Allah.
"Alone, with no partner" means: There is no partner with Him in His divinity, lordship, names, and attributes.
"To Him belongs the dominion" means: The absolute, general, inclusive, and all-encompassing dominion, the dominion of the heavens and the earth and what is between them belongs to Him.
"And praise is due to Him" means: The absolute perfection belongs to Him, and He is the One praised for His perfection out of love and exaltation in all conditions, good or bad.
"And He has power over all things" means His power is complete and absolute in every aspect, and nothing escapes His power or can resist His Will.
"There is no power or strength except through Allah" means There cannot be any shift from one condition to another and from disobedience to Allah to obedience to Him, and there is no power except through Allah; He is the One Who gives help and should be relied upon.
"There is no god but Allah, and we worship none but Him": It affirms the meaning of divinity and the negation of polytheism and that none but Him deserves to be worshiped.
"To Him belongs the favor, to Him belongs the grace": He is the One Who creates the blessings and possesses them and He bestows them, as a favor from Him, upon whomever of His servants He wishes.
"And to Him belongs all excellent praise": For His essence, attributes, actions, and blessings, and for every condition.
"There is no god but Allah; we are sincerely devoted to Him" means that we are believers in His Oneness, without showing off or pursuing a good reputation among people for our obedience to Allah.
"Even if the disbelievers may dislike it" means: We firmly adhere to the belief in Allah's Oneness, even if the disbelievers detest it.