Isaiah 7:4-6, 14

and say unto him, Take heed, and be quiet; fear not, neither let thy heart be faint, because of these two tails of smoking firebrands, for the fierce anger of Rezin and Syria, and of the son of Remaliah. Because Syria, Ephraim, and the son of Remaliah, have purposed evil against thee, saying, Let us go up against Judah, and vex it, and let us make a breach therein for us, and set up a king in the midst of it, even the son of Tabeel

Therefore the Lord himself will give you a sign: behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.