Wikipedia: Phos Hilaron (Koinē Greek: Φῶς Ἱλαρόν, romanized: Fόs Ilarόn) is an ancient Christian hymn originally written in Koine Greek. Often referred to in the Western Church by its Latin title Lumen Hilare, it has been translated into English as O Gladsome Light. It is the earliest known Christian hymn recorded outside of the Bible that is still in use today. The hymn is part of vespers in the Byzantine Rite, and also included in Catholic and some modern Anglican and Lutheran liturgies.
Figured might as well throw this in, given its historical significance.
Wish I could've found a better recording, but all the cleanest ones are in English.
Φῶς ἱλαρὸν ἁγίας δόξης ἀθανάτου Πατρός,
οὐρανίου, ἁγίου, μάκαρος, Ἰησοῦ Χριστέ,
ἐλθόντες ἐπὶ τὴν ἡλίου δύσιν, ἰδόντες φῶς ἑσπερινόν,
ὑμνοῦμεν Πατέρα, Υἱόν, καὶ ἅγιον Πνεῦμα, Θεόν.
Ἄξιόν σε ἐν πᾶσι καιροῖς ὑμνεῖσθαι φωναῖς αἰσίαις,
Υἱὲ Θεοῦ, ζωὴν ὁ διδούς· διὸ ὁ κόσμος σὲ δοξάζει.
O Light gladsome of the holy glory of the Immortal Father,
the Heavenly, the Holy, the Blessed, O Jesus Christ,
having come upon the setting of the sun, having seen the light of the evening,
we praise the Father, the Son, and the Holy Spirit: God.
Worthy it is at all times to praise Thee in joyful voices,
O Son of God, Giver of Life, for which the world glorifies Thee.
(wikipedia)