Musnad Ahmad 28:265

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from 'Amr ibn Shu'ayb, from his father, from his grandfather, who said: The Prophet, peace and blessings of Allah be upon him, heard a people disputing, so he said: "Those who were before you only perished because of this; they struck some of the Book of Allah against others. The Book of Allah was only revealed for some of it to confirm others, so do not belie some of it with others. Whatever you know of it, then speak [of it], and whatever you are ignorant of, then refer it to its Knower."