Mishkat al-Masabih 4 Prayer كتاب الصلاة 686

وَعَنْ أُبَيِّ بْنِ كَعْبٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا سَلَّمَ فِي الْوتر قَالَ: «سُبْحَانَكَ الْمَلِكِ الْقُدُّوسِ» رَوَاهُ أَبُو دَاوُدَ وَالنَّسَائِيُّ وَزَادَ: ثَلَاث مَرَّات يُطِيل فِي آخِرهنَّ وَفِي رِوَايَةٍ لِلنَّسَائِيِّ عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبْزَى عَنْ أَبِيهِ قَالَ: كَانَ يَقُولُ إِذَا سَلَّمَ: «سُبْحَانَ الْمَلِكِ الْقُدُّوسِ» ثَلَاثًا وَيَرْفَعُ صَوْتَهُ بالثالثة

Ubayy b. Ka’b said that when God’s Messenger gave the salutation in the witr he said, “Glory be to the King most holy.” Abu Dawud and Nasa’i transmitted it, Nasa’i adding that he said it three times, prolonging the words. In a version by Nasa’i from ‘Abd ar-Rahman b. Abza from his father, he said that he used to say three times when he uttered that salutation, “Glory be to the King most holy”, raising his voice when saying it the third time.