not for one moment
Not for any length of time; not at any point; not at all or in any capacity. Not for one moment did I think this would be a winning ticket, so I was totally gobsmacked to find out I'd won the jackpot! A: "So, did you suspect we were throwing you a surprise party?" B: "No, not for one moment!"
not for a/one ˈminute/ˈmoment/ˈsecond/ˈinstant
(informal) not at all; definitely not: I didn’t think for a minute that he was married.Not for one instant would I ever consider going there on holiday again.