Musnad Ahmad 30:2660

Yazid ibn Harun narrated to us, he said: Ibn Abi Dhi'b informed us, and Hashim ibn al-Qasim, from Ibn Abi Dhi'b, from al-Maqburi, from Abu Hurairah, from the Prophet, may Allah bless him and grant him peace, that he said regarding the Mother of the Quran: "It is the Mother of the Quran, and it is the seven oft-repeated verses, and it is the Great Quran."