Revelation 3:20 says: Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
(KJV).
The verse appears in the letter to the church at Laodicea in Revelation 3. Read it in context at Revelation 3:20, or the full chapter at Revelation 3.