Council of Chalcedon, 451 A.D., Act V

Therefore, following the holy fathers, we all with one accord teach men to acknowledge one
and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in
manhood, truly God and truly man, consisting also of a reasonable soul and body, of one
substance (homoousios) with the Father as regards his Godhead, and at the same time of
one substance with us as regards his manhood; like us in all respects, apart from sin; as
regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood
begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer
(Theotokos); one and the same Christ, Son, Lord, Only-begotten, recognized in two
natures, without confusion, without change, without division, without separation; the
distinction of natures being in no way annulled by the union, but rather the characteristics
of each nature being preserved and coming together to form one person and subsistence,
not as parted or separated into two persons, but one and the same Son and Only-begotten
God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him,
and our Lord Jesus Christ himself taught us, and the creed of the Fathers has handed down
to us.