《商君书·境内》
没有军役的时候，庶子每月为其大夫服役六天。有军役的时候，根据实际情况役使庶子。
其无役事也，其庶子役其大夫月六日；其役事也，随而养之军。
When not on military duty, shu sons served their lords for six days in a month. When on campaign, shu sons were requisitioned as necessary.