Where are Validator error messages stored in Laravel?

I have the following code in a blade file:

@if($errors->has('password_again'))
    <div class="error">
        * {{ $errors->first('password_again') }}
    </div>
@endif

This line:

{{ $errors->first('password_again') }}

Displays:

"The password again field is required."

However I can't seem to find this string anywhere. I've looked in the Controller file which calls this blade and just went through a ton of files searching for the string and can't seem to find it. Which file should I be looking in to edit this string?