Use featured image in post navigation

[pross (Pross With Spaces)]

add_filter( 'fl_theme_builder_post_nav', function( $args ) {

	$next_post     = get_next_post();
	$previous_post = get_previous_post();
	if ( isset( $next_post->ID ) ) {
		$args['next_text'] = '<span class="post-title">%title</span>' . get_the_post_thumbnail( $next_post->ID, 'thumbnail' );
	}
	if ( isset( $previous_post->ID ) ) {
		$args['prev_text'] = '<span class="post-title">%title</span>' . get_the_post_thumbnail( $previous_post->ID, 'thumbnail' );
	}
	return $args;
} );