beyond the/a shadow of (a) doubt
With certainty; for sure. I only made such a big change in my life because I knew beyond the shadow of a doubt that it was the right thing for me to do.
beyond/without a ˌshadow of (a) ˈdoubt
, there isn’t a ˌshadow of a ˈdoubt (that...)
there is no doubt at all (that...); absolutely certainly: He’s innocent beyond a shadow of a doubt.There isn’t a shadow of doubt in my mind about the safety of the system.