See too Matthew 2:13, 19-20 for additional passages but I am sure there must be more.
Matthew 1:19 - 20
ESV - 19 And her husband Joseph, being a just man and unwilling to put her to shame, resolved to divorce her quietly. 20 But as he considered these things, behold, an angel of the Lord appeared to him in a dream, saying, "Joseph, son of David, do not fear to take Mary as your wife, for that which is conceived in her is from the Holy Spirit.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.