Mishkat al-Masabih #156

Abu Rafi‘ reported God’s messenger as saying, “Let me not find one of you reclining on his couch when he hears something regard which I have commanded or forbidden and saying, ‘I do not know, we found in God’s Book we have followed.’ ” Ahmad, Tirmidhi, A Dawud, Ibn Majah, and Baihaqi (in Dala’il an-nubuwa) transmitted it.