Musnad Ahmad 482:28

Hassan ibn Musa narrated to us, he said: Ibn Lahi'ah narrated to us, he said: Abu Qabil narrated to us, he said: I heard Uqbah ibn Amir saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "I only fear for my nation the Book and the milk." It was said: O Messenger of Allah, what is the matter with the Book? He said: "The hypocrites will learn it, then they will argue with it against those who believe." It was said: And what is the matter with the milk? He said: "People who love milk, so they will depart from the congregations and abandon the Friday prayers."