You're probably thinking of Jesus' comment, pointing out that lying is part of the devil's character (just as truth is part of God's character). He said, "When he lies, he speaks his native language, for he is a liar and the father of lies" (John 8:44).
At times, however, the devil can be very convincing! After all, he doesn't usually come to us and say, "Listen! What I'm about to tempt you to do is a lie, and will lead you down the path to destruction!" No, he is very clever, and he will do everything in his power to convince us that his way is best -- and God's way is wrong. If we could see for even one second where he is leading us, we'd never follow him. But we willfully turn our backs on the truth, and instead believe his lies.
What is his greatest lie? It's that we should believe him instead of God. In the Garden of Eden, he persuaded Adam and Eve to believe him instead of God -- and it led to their deaths. In the wilderness, he tried to deceive Jesus into following him instead of God (although he failed). In the last days, the Bible says, Satan's followers will end up being deceived -- and deceiving others (see 2 Timothy 3:13).
Only God can save us, and He made this possible by sending His Son, Jesus Christ, into the world to give His life for us. Make sure of your commitment to Him -- and then let the truth of His Word, the Bible, guide your steps every day.