post hoc, ergo propter hoc

Latin phrase

post hoc, er·​go prop·​ter hoc ˈpȯst-ˌhōk ˌer-gō-ˈprȯp-ter-ˌhōk 

: after this, therefore because of this : because an event occurred first, it must have caused this later event

—used to describe a fallacious argument