This well-known prayer is in various prayer books - usually in Morning Prayer. Personally, I think its a great prayer at bed-time!
O God, the author of peace and lover of concord,
to know you is eternal life,
to serve you is perfect freedom:
defend us your servants from all assaults of our enemies,
that we may trust in your defence
and not fear the power of any adversaries;
through Jesus Christ our Lord. Amen.