Homily on the Holy Nativity of Christ, 5 — as quoted by Pitre (p 113)
Those who love Christ refuse to hear that the Mother of God ceased to be a virgin at a particular moment.
No freely usable English translation of this passage is online, so the note keeps Pitre's quotation and links to the full text. Translation: as quoted by Pitre (via Gambero, Mary and the Fathers of the Church).
In Jewish Roots of Mary
Why it is cited
'Those who love Christ refuse to hear that the Mother of God ceased to be a virgin at a particular moment.' Basil shows the perpetual virginity treated as a mark of orthodoxy.