Said in the sacrament of Reconciliation after the penitent's confession. The classical English form, in use since at least the 18th century.
Catholic · Modern (18th c.–today)
Act of Contrition
O my God, I am heartily sorry for having offended thee,
and I detest all my sins,
because of thy just punishments,
but most of all because they offend thee, my God,
who art all good and deserving of all my love.
I firmly resolve, with the help of thy grace,
to sin no more and to avoid the near occasion of sin. Amen.