The Prophet (ﷺ) used to recite this dhikr three times at the end of the Witr prayer, and the last time he would say it at length:
سُبْحَانَ الْمَلِكِ الْقُّدُّوْسِ
Pronunciation
Subhaanal-Malikil-Quddoos
Meaning
Glory is to the King, the Holy.
Source: Sahih (Albani). Abu Dawud No. 1430; An-Nasa'i No. 1699, 1701
Read the hadith
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي عُبَيْدَةَ، حَدَّثَنَا أَبِي، عَنِ الأَعْمَشِ، عَنْ طَلْحَةَ الأَيَامِيِّ، عَنْ ذَرٍّ، عَنْ سَعِيدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ أَبْزَى، عَنْ أَبِيهِ، عَنْ أُبَىِّ بْنِ كَعْبٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا سَلَّمَ فِي الْوِتْرِ قَالَ " سُبْحَانَ الْمَلِكِ الْقُدُّوسِ " .
Narrated Ubayy ibn Ka'b: When the Messenger of Allah (ﷺ) offered salutation in the witr prayer, he said: Glorify be to the king most holy. Sunan Abi Dawud 1430 [Sahih (Albani). Abu Dawud No. 1430; An-Nasa'i No. 1699, 1701]
Duas from IslamicAPI's Masnun Dua dataset (based on the Quran, hadith, Hisnul Muslim and Rahe Belayat). See the dataset