Musnad Ahmad 31:508

Yahya narrated to us, from al-Taymi, Abu Nadra narrated to us, from Abu Sa’id, from the Prophet, may God bless him and grant him peace, who said: "Let not the awe of people prevent any one of you from speaking the truth when he sees it, witnesses it, or hears it." Abu Sa’id said: "I wish I had not heard it." And Abu Nadra said: "I wish I had not heard it."