It is narrated from Sayyiduna Jabir bin Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to recite in the Fajr prayer Surah "Qaf, wa al-Qur'an al-Majid", and after that his (peace and blessings be upon him) prayer became lighter.
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1916