For you are the children of your father the devil, and you love to do the evil things he does. He was a murderer from the beginning. He has always hated the truth, because there is no truth in him. When he lies, it is consistent with his character; for he is a liar and the father of lies.
John 8:44 NLT
When Jesus spoke to these people, He was talking to the religious leaders of this time. God doesn't need to validate the truth through the words of mankind. He, who already knows motive and intent, looks at our hearts. Our God is a God of truth. That is His character and can be ours too when we seek to know Him. Still He knows the way of evil and deception and is well acquainted with those who bear that character. Whom will you believe? Who is your Daddy?
And no wonder, for Satan himself masquerades as an angel of light.
2 Corinthians 11:14 NIV