Here’s a prayer for unity based on John 17, Jesus’ high-priestly prayer. It was written by William Temple.
Prayer of Petition
Lord Jesus Christ,
who prayed for your disciples that they might be one,
even as you are one with the Father;
draw us to yourself,
that in common love and obedience to you
we may be united to one another,
in the fellowship of the one Spirit,
that the world may believe that you are Lord,
to the glory of God the Father. Amen.
— written by William Temple (1881-1944).