Musnad Ahmad 915:2

Abdullah narrated to us, he said: Ismail Abu Ma'mar narrated to me, he said: Abu Usamah narrated to us, from Abd al-Hamid ibn Ja'far, from al-Ala' ibn Abd al-Rahman, from his father, from Abu Hurayrah, from Ubayy ibn Ka'b, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Shall I not teach you a surah, the like of which has not been revealed in the Torah, nor in the Zabur, nor in the Injil, nor in the Quran?" I said: "Yes." He said: "I hope that I will not go out of that door until you know it." Then the Messenger of Allah stood up, and I stood up with him. He took my hand and began to speak to me until he reached near the door. I reminded him and said: "O Messenger of Allah, the surah you told me about?" He said: "How do you recite when you stand to pray?" So I recited the Opening of the Book (Fatihat al-Kitab). He said: "It is it, it is it, and it is the seven oft-repeated verses, and the Great Quran which I have been given." Abdullah said: I asked my father about al-Ala' ibn Abd al-Rahman and Suhayl ibn Abi Salih, and he prioritized al-Ala' over Suhayl, and said: "I have not heard anyone mention al-Ala' with evil." And Abu Abd al-Rahman said: "And Abu Salih is more beloved to me than al-Ala'."