I’ve found an answer:
<?php
$cats = get_the_category();
$args = array(
'post_type' => 'article',
'post__not_in' => array( get_the_ID() ),
'posts_per_page' => 5,
'cat' => $cats[0]->term_id,
'meta_query' => array(
array(
'key' => 'recommended_article',
'value' => '1',
'compare' => '=='
)
)
);
$query = new WP_Query( $args );
?>
<?php if( $query->have_posts() ) : while( $query->have_posts() ) : $query->the_post(); ?>
<!--HTML-->
<?php endwhile; endif; wp_reset_postdata(); ?>