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.

Verbatim translation

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.

According to Wikipedia, this is the oldest Christian hymn, not in the Bible, to still be used in worship services today.