It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Qul huwa Allahu ahad is equal to a third of the Qur'an, and Qul ya ayyuha al-kafirun is equal to a quarter of the Qur'an," and he (peace and blessings be upon him) used to recite these two surahs in the two rak'ahs of Fajr, and he said: "In these two rak'ahs lies what is desirable for all time."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13436