God forbid
A phrase invoking God's protection to keep something from happening. Sometimes used sarcastically or hyperbolically. God forbid I get another ticket on my parents' car. I'll be grounded for a month! God forbid that an R-rated film should have anything offensive in it!
God forbid!
and Heaven forbid!a phrase expressing the desire that God would forbid the situation that the speaker has just mentioned from ever happening. Tom: It looks like taxes are going up again. Bob: God forbid! Bob: Bill was in a car wreck. I hope he wasn't hurt! Sue: God forbid!