It is narrated from Jabir bin Samurah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) recited in the Fajr prayer: "Qaf. By the glorious Qur'an" [Surah Qaf: 1], and after that his prayer was lighter.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4012