سنن النسائي

Mansur reported from Salamah bin Kuhail, from Sa'eed bin Abdur-Rahman bin Abza, from his father, who said: "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."