Here’s a prayer for peace from the PCUSA website.
Prayer in Times of Violence and Fear
Almighty, all-merciful God,
through Christ Jesus you have taught us to love one another,
to love our neighbors as ourselves,
and even to love our enemies.
In times of violence and fear,
let the peace of Christ rule in our hearts,
so that we may not be overcome with evil
but overcome evil with good.
Help us to see each person in light of the love and grace
you have shown us in Christ.
Put away the nightmares of terror
and awaken us to the dawning of your new creation.
justice is done with mercy, and all are reconciled.
We ask these things in the name
and for the sake of Jesus Christ our Lord. Amen.
~ From a collection of Prayers for Times of National and International Crisis and Tragedy, posted on the PCUSA website. http://www.pcusa.org/