Psalm 139:4 (ESV)

4 Even before a word is on my tongue, behold, O LORD, you know it altogether.

In the Hebrew language, two strong words are used here (even and behold), which both emphasize that it is absolutely certain that the Lord knows my every word and my every thought.

God knows what I say or think already before the words are on my tongue! The farthest corners of my heart are not hidden from him.