Q:

Unable to disable a startup message in Zsh

I get the following when I start my Zsh.
Usage: prompt <options>
Options:
    -c              Show currently selected theme and parameters
    -l              List currently available prompt themes
    -p [<themes>]   Preview given themes (defaults to all)
    -h [<theme>]    Display help (for given theme)
    -s <theme>      Set and save theme
    <theme>         Switch to new theme immediately (changes not saved)

It seems to be set by some theme file, since the same text is here.
How can you disable the notification in Zsh?

A:

This isn't a startup message. It's the error/default help message displayed when the prompt command is used without arguments or erroneous arguments. Find out where you're using it, and fix/delete it.

