absit omen
interjection
ab·sit omen
ˌabsə̇tˈōmən
—used as a mild invocation
if he should fail, absit omen, all will be lost
compare God forbid at god entry 2 
Word History
Etymology
Latin, may (evil) omen be absent, i.e., may what is said not come true
First Known Use
1594, in the meaning defined above