King James Bible
"Ye have heard that it was said by them of old time, Thou shalt not commit adultery:"
Jesus introduces a formula he uses throughout the Sermon on the Mount to contrast traditional interpretations with his authoritative teaching. The phrase acknowledges the oral tradition of rabbinic instruction that interpreted the written Law for everyday application. This quotes the seventh commandment from Exodus 20:14, which protected the marriage covenant and family structure in ancient Israel. Jesus prepares to expand this external prohibition to address the internal desires and thoughts that lead to such actions.