This is an unhappy expression, bringing in the name of God where it does not occur. In the O.T. it is chalilah, 'far be it.' Ge 44:7,17, etc. In the N.T. ?? ???????, 'let it not be.' Ro 3:4,6,31, etc.
And they answered him, "Wherefore saith my lord such words? God forbid that thy servants should do so.
And he answered, "God forbid that I should do so, the man with whom the cup is found, he shall be my servant: but go ye in peace unto your father."
God forbid. Let God be true, and all men liars, as it is written, "That thou mightest be justified in thy sayings and shouldest overcome when thou art judged."