$re = '/(\G(?!^)|\"body\"\s*:\s*\")([^\",\\\\]*(?:\\\\.[^\",\\\\]*)*),/m';
$str = '{
"url": "RETURNED URL",
"repository_url": "RETURNED URL",
"labels_url": "RETURNED URL",
"comments_url": "RETURNED URL",
"events_url": "RETURNED URL",
"html_url": "RETURNED URL",
"id": "RETURNED_ID",
"node_id": "RETURNED id",
"number": 10,
...
"author_association": "xxxx",
"active_lock_reason": null,
"body": "text \\"text\\" text, text text, text \\\\\\"text text\\", text, text text",
"performed_via_github_app": null
}';
$subst = "$1$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php