I beg to differ

US /aɪ bɛɡ tə ˈdɪfər/
UK /aɪ bɛɡ tə ˈdɪfər/
"I beg to differ" picture
1.

a polite way of saying that you do not agree with someone

:
You say it's a good idea, but I beg to differ.
He claimed the report was accurate, but I beg to differ.