'Witness' in the Bible

For God is my witness, whom I serve in my spirit in the gospel of his Son, how unceasingly I make mention of you, always in my prayers

in that they show the work of the law written in their hearts, their conscience bearing witness therewith, and their thoughts one with another accusing or else excusing them );

The Spirit himself beareth witness with our spirit, that we are children of God:

I say the truth in Christ, I lie not, my conscience bearing witness with me in the Holy Spirit,

For I bear them witness that they have a zeal for God, but not according to knowledge.