I never knew you

Where do we find the words in scripture "I never knew you" 
Jesus Himself
 “Not everyone who says to Me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven. “Many will say to Me in that day, ‘Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?’  “And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!’ Matt 7:21-23

Who was He reffering to?
Those who say Lord Lord, those who have prophecied and cast out demons and done many wonders in the name of the Lord.
These thing mean nothing though if the one doing them practices lawlessness.

What is lawlessness?
1John 3 and verse 4 says "sin is lawlessness."

Jesus died and rose again overcoming sin and death. Those believing in Him and remaining in Him live to bear good fruit,(righteousness) in order to please the Father. As we read through 1John 3 it is clear that sin is no acceptable and that Christ followers are to practice righteousness.
An unsaved person has no choice about sin, they will sin. The saved, those who are born again of God on the other hand are to walk in newness of life, no longer living for themselves as Christ is to live in them and out of them.
So does this mean that a Christian will never sin? No.
It means they should not practice or continue in sin.
The Christians walk is always to die to self but there are going to be times when things happen and we will sin. Paul says   "For the good that I will [to do,] I do not do; but the evil I will not [to do,] that I practice. Now if I do what I will not [to do,] it is no longer I who do it, but sin that dwells in me. I find then a law, that evil is present with me, the one who wills to do good. For I delight in the law of God according to the inward man. But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members."Rom 7:19-23.
Other examples include James 3:2, Phil 3:12. Don't forget also that Noah, Abraham, Moses, David, Samson and many more old testament saints sinned.
1Cor 6:8-12