Which phrase is correct? "Oh, God forbid." or "Oh, God forbids."
TV show context:
Father: The men and women of this hospital live in separate wards for good reason. In the past there have been incidents of violence and indecent behavior.
Daughter: Oh, God forbid!

Why is the subject-verb agreement not followed?
Thanks for your answer.

Question

Which phrase is correct? "Oh, God forbid." or "Oh, God forbids."
TV show context:
Father: The men and women of this hospital live in separate wards for good reason. In the past there have been incidents of violence and indecent behavior. 
Daughter: Oh, God forbid!

Why is the subject-verb agreement not followed? 
Thanks for your answer.

Answer

This is a shortened form of "May God forbid [this]."

Here is a related discussion of the subjunctive in phrases such as "God bless you."

https://www.italki.com/question/472405

Answer

"Oh, God forbid!"
Because it is in imperative form.
Same for "God bless you".

Answer

God forbid
https://dictionary.cambridge.org/dictionary/english/god-forbid
>>subject-verb agreement not followed? 
It's an idiom aka tradition.

لا تفوّت فرصة تعلّم لغة جديدة وأنت مرتاح في منزلك. تصفّح مجموعتنا المختارة من مدرّسي اللغات ذوي الخبرة وسجّل في درسك الأول الآن!