The Te Deum Prayer / Hymn
The historical prayer hymn "Te Deum Laudamus" (God We Praise You), dating back to the late 300's A.D., and authorship is attributed to a handful of writers dating from the same time period including St. Augustine, St. Ambrose, or St. Hilary of Poitiers. It has been widely used in Protestant, Catholic, and Orthodox circles. It is often simply referred to as "the Te Deum".
In the Liturgy of the Hours revision promulgated by Pope Paul VI (the current version in use in the Catholic church), the "Te Deum" is sung at the end of the Office of Readings on all Sundays except those in Lent, on all Solemnities and Feasts, and during the octaves of Easter and Christmas. Here is the prayer:
You are God: we praise you; You are the Lord; we acclaim you;
You are the eternal Father: All creation worships you.
To you all angels, all the powers of heaven, Cherubim and Seraphim, sing in endless praise: Holy, holy, holy Lord, God of power and might, heaven and earth are full of your glory.
The glorious company of apostles praise you.
The noble fellowship of prophets praise you.
The white-robed army of martyrs praise you.
Throughout the world the holy Church acclaims you;
Father, of majesty unbounded, your true and only Son, worthy of all worship, and the Holy Spirit, advocate and guide.
You, Christ, are the king of glory, the eternal Son of the Father.
When you became man to set us free you did not shun the Virgin's womb.
You overcame the sting of death and opened the kingdom of heaven to all believers.
You are seated at God's right hand in glory. We believe that you will come and be our judge.
Come then, Lord, and help your people, bought with the price of your own blood,
and bring us with your saints to glory everlasting.