'It is I' in the Bible

Then Abner looked behind him and said, “Is that you, Asahel?” And he answered, “It is I.”

Nathan then said to David, “You are the man! Thus says the Lord God of Israel, ‘It is I who anointed you king over Israel and it is I who delivered you from the hand of Saul.

Then David spoke to the Lord when he saw the angel who was striking down the people, and said, “Behold, it is I who have sinned, and it is I who have done wrong; but these sheep, what have they done? Please let Your hand be against me and against my father’s house.”