Musannaf Ibn Abi Shayba 37:640

Humaid ibn Abd al-Rahman narrated to us, from Hasan, from Abd al-Malik ibn Abi Sulayman, who said: I asked Abu Ja'far, "Is there disbelief (kufr) in this nation?" He said, "I do not know of it, nor polytheism (shirk)." I said, "Then what is it?" He said, "Transgression (baghy)."