Musnad Ahmad 482:130

Zayd ibn al-Hubab narrated to us, Abu al-Samh narrated to me, Abu Qubayl narrated to me, that he heard Uqbah ibn Amir saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, I fear two things for my nation: the Quran and milk. As for milk, they will seek the countryside, follow desires, and abandon prayers. And as for the Quran, the hypocrites will learn it and argue with it against the believers."