"Do not think that I [Jesus] have come to abolish the Law (the Old Testament) or the Prophets; I have not come to abolish them but to fulfill them.  I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke or a pen, will by any means disappear from the Law (the Old Testament) until everything is accomplished.  (Matthew 5:17-18)" 

"Then Jesus said to the crowds and to his disciples: 'The teachers of the law and the Pharisees sit in Moses' seat.  So you must obey them and do everything they tell you. But do not do what they do, for they do not practice what they preach.'  (Matthew 23:1-3)"