Limit SearchWP results to a single author

gistfile1.php

<?php
 
function searchwp_include_only_author( $ids, $engine, $terms ) {
  $authorID = 8; // limit to author 8
 
  // get the IDs of all the posts in this category
  $args = array( 
    'author' => $authorID, 
    'fields' => 'ids' 
  );
  $posts = new WP_Query( $args );
  
  return $posts->posts;
}
 
add_filter( 'searchwp_include', 'searchwp_include_only_author', 10, 3 );