6 I am, however, addressing not merely men who fail to do what they are commanded, but the members of a deluded sect. For the precepts of Manichæus are such that, if you do not keep them, you are deceivers; if you do keep them, you are deceived. Christ never taught you that you should not pluck a vegetable for fear of committing homicide; for when His disciples were hungry when passing through a field of grain, He did not forbid them to pluck the ears on the Sabbath day; which was a rebuke to the Jews of the time since the action was on Sabbath; and a rebuke in the action itself to the future Manichæans. The precept of Manichæus, however, only requires you to do nothing while others commit homicide for you; though the real homicide is that of ruining miserable souls by such doctrines of devils.
Source: Reply to Faustus the Manichaean (New Advent)