10 You shall not slander any man, lest they call you Satan. If you hate the name, go not near to the act; but if you love the act, be not angry at the name. Count yourself rebuked first of all by the beasts and birds, how that every kind cleaves to its kind; and so agree with your yokefellow. Rejoice not in men's dishonour, that you become not a Satan yourself. If evil should happen to him that hates you, see that you rejoice not, lest you sin. If your adversary should fall, be in pain and mourning. Keep your heart with all diligence, that it sin not in secret; for there is to be a laying bare of thoughts and of actions. Employ your hands in labour, and let your heart meditate in prayer. Love not vain discourse, for discourse that shall be profitable alike to the soul and the body lightens the burden of your labour.
Source: On Admonition and Repentance (New Advent)