Musnad Abu Ya'la al-Mawsili 155:57

Uthman ibn Abi Shaybah narrated to us, Yahya ibn Ya'la al-Taymi narrated to us, Mansur narrated to us, from Sa'd ibn Ibrahim, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Disputation regarding the Quran is disbelief."