What is the earliest recorded instance where Mary is called "Blessed Virgin?"

I was recently spending some thought on this topic which came from this question: https://christianity.stackexchange.com/questions/35105/to-most-protestants-what-is-the-understanding-of-luke-148-kjv I answered the question and proposed as an afterthought that people cynical of Catholic Tradition would quickly dismiss the significance that Mary is called blessed as a self-fulfilling prophecy. I'm not sure yet how this might help that argument either way, but what is the earliest instance (outside of Luke's gospel) of Mary being called "Blessed Virgin" or some variation involving the word "blessed"? Since the Lucan story specifically states that "**all** generations will call me blessed", I don't want a quote from Luke or any work that just retells the story. I mean any works from later writers that explicitly call Mary "blessed"; that is, examples of further generations calling Mary blessed. If it so happens that such statements evolved to their current state I would like to see a few examples showing that evolution.