"The Virgin Mary, being obedient to his word, received from an angel the glad tidings that she would bear God" (Against Heresies, 5:19:1 [A.D. 189])." Irenaeus
"The Father bears witness from heaven to his Son. The Holy Spirit bears witness, coming down bodily in the form of a dove. The archangel Gabriel bears witness, bringing the good tidings to Mary. The Virgin Mother of God bears witness" (Catechetical Lectures 10:19 [A.D. 350]). Cyril of Jerusalem
"The Word begotten of the Father from on high, inexpressibly, inexplicably, incomprehensibly, and eternally, is he that is born in time here below of the Virgin Mary, the Mother of God" (The Incarnation of the Word of God 8 [A.D. 365]). Athanasius
We confess, then, our Lord Jesus Christ, the only begotten Son of God, perfect God and perfect man, of a rational soul and a body, begotten before all ages from the Father in his Godhead, the same in the last days, for us and for our salvation, born of Mary the Virgin according to his humanity, one and the same consubstantial with the Father in Godhead and consubstantial with us in humanity, for a union of two natures took place. Therefore we confess one Christ, one Son, one Lord. According to this understanding of the unconfused union, we confess the holy Virgin to be the Mother of God because God the Word took flesh and became man and from his very conception united to himself the temple he took from her" (Formula of Union [A.D.431] Council of Ephusus
"I have been amazed that some are utterly in doubt as to whether or not the holy Virgin is able to be called the Mother of God. For if our Lord Jesus Christ is God, how should the holy Virgin who bore him not be the Mother of God?" (Letter to the Monks of Egypt 1 [A.D. 427]). Cyril of Alexandria
"If anyone does not agree that holy Mary is Mother of God, he is at odds with the Godhead" (Letter to Cledonius the Priest 101 [A.D. 382] Gregory of Nazianz