Second Council of Constantinople, Capitulum II

If anyone shall not confess that the Word of God has two nativities, the one from all eternity of the Father, without time and without body; the other in these last days, coming down from heaven and being made flesh of the holy and glorious Mary, Mother of God and always a virgin, and born of her:  let him be anathema.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.