1741. Sunan an-Nasa’i Chapter: Encouragement to pray in houses and the virtue of doing so; Book 20, Hadith 144

Ishawq bin Mansur informed us, he said: “Abu Dawud narrated to us, he said: Shu’ba narrated to us, from Qatadah, from Abdur-Rahman bin Abza, that
The Messenger of Allah (ﷺ) used to recite in witr: Glorify the Name of your Lord, the Most High;” and “Say: O you disbelievers!;’ and ‘Say: He is Allah, (the) One.’ And when he said the taslim, he would say: Subhanal-Malikil-Quddus (Glory be to the Sovereign, the Most Holy) three times, elongating his words the third time.”