The Prophet ﷺ used to recite "Qaf. By the glorious Quran" [Qaf 50:1] in the dawn prayer, and his prayers afterward were lighter.
إن النبي ﷺ كان يقرأ في الفجر {ق والقرءان المجيد} وكان صلاته بعد تخفيفا.
Muslim narrated it in the Book of Prayer (458), from Abu Bakr bin Abu Shayba, who said, Husayn bin Ali narrated to us, from Zaida, who said, Simak bin Harb narrated to us, from Jabir bin Samura, and he mentioned it.