The oldest hymn to the Theotokos

                                        
The oldest prayer we know of dedicated to the Virgin Mary is known as "Beneath thy compassion" (Greek: Ὑπὸ τὴν σὴν εὐσπλαγχνίαν; Latin: Sub tuum praesidium). 
The earliest text of this hymn was found in a Christmas liturgy of the third century. 
It is written in Greek and dates to approximately 250 A.D. 

For Orthodox, the hymn is sung as the last dismissal hymn of daily Vespers during Great Lent.

The entire hymn in Greek reads:

Ὑπὸ τὴν σὴν εὐσπλαγχνίαν,
καταφεύγομεν, Θεοτόκε.
Τὰς ἡμῶν ἱκεσίας,
μὴ παρίδῃς ἐν περιστάσει,
ἀλλ᾽ ἐκ κινδύνων λύτρωσαι ἡμᾶς,
μόνη Ἁγνή, μόνη εὐλογημένη. 

In English:

Beneath thy compassion,
We take refuge, O Mother of God:
do not despise our petitions in time of trouble,
but rescue us from dangers,
only pure one, only blessed one. 

Church Slavonic

Подъ твою милость,

прибѣгаемъ богородице дѣво,

молитвъ нашихъ не презри в скорбѣхъ.

но ѿ бѣдъ избави насъ,

едина чистаѧ и благословеннаѧ.

Latin text

Sub tuum praesidium

confugimus,

Sancta Dei Genetrix.

Nostras deprecationes ne despicias

in necessitatibus nostris,

sed a periculis cunctis

libera nos semper,

Virgo gloriosa et benedicta