Musannaf Ibn Abi Shayba 37:505

Waki' narrated to us, from Sufyan, from Habib, from Abu al-Bakhtari, who said: It was said to Hudhayfah, "Shall we not enjoin the good and forbid the evil?" He said, "It is indeed good, but it is not from the Sunnah to raise the weapon against your Imam."