'O God' in the Bible

But we made our prayer to God, and had men on watch against them day and night because of them.

For they were hoping to put fear in us, saying, Their hands will become feeble and give up the work so that it may not get done. But now, O God, make my hands strong.

For in the days of David and Asaph in the past, there was a master of the music, and songs of blessing and praise to God.