Honestly asking, what's wrong with "Password (Leave empty if you're using {Name of SSO}): ____"?
If you are going to tell that may confuse users, I think not having a password field is already confusing the other half, while also not being password-manager-friendly.
If you are going to tell that may confuse users, I think not having a password field is already confusing the other half, while also not being password-manager-friendly.