He returns to explain the prophecy of Isaiah
Trypho: I admit that such and so great arguments are sufficient to persuade one; but I wish [you] to know that I ask you for the proof which you have frequently proposed to give me. Proceed then to make this plain to us, that we may see how you prove that that [passage] refers to this Christ of yours. For we assert that the prophecy relates to Hezekiah.
Justin: I shall do as you wish. But show me yourselves first of all how it is said of Hezekiah, that before he knew how to call father or mother, he received the power of Damascus and the spoils of Samaria in the presence of the king of Assyria. For it will not be conceded to you, as you wish to explain it, that Hezekiah waged war with the inhabitants of Damascus and Samaria in presence of the king of Assyria. 'For before the child knows how to call father or mother,' the prophetic word said, 'He shall take the power of Damascus and spoils of Samaria in presence of the king of Assyria.' For if the Spirit of prophecy had not made the statement with an addition, 'Before the child knows how to call father or mother, he shall take the power of Damascus and spoils of Samaria,' but had only said, 'And shall bear a son, and he shall take the power of Damascus and spoils of Samaria,' then you might say that God foretold that he would take these things, since He foreknew it. But now the prophecy has stated it with this addition: 'Before the child knows how to call father or mother, he shall take the power of Damascus and spoils of Samaria.' And you cannot prove that such a thing ever happened to any one among the Jews. But we are able to prove that it happened in the case of our Christ. For at the time of His birth, Magi who came from Arabia worshipped Him, coming first to Herod, who then was sovereign in your land, and whom the Scripture calls king of Assyria on account of his ungodly and sinful character. For you know that the Holy Spirit oftentimes announces such events by parables and similitudes; just as He did towards all the people in Jerusalem, frequently saying to them, 'Your father is an Amorite, and your mother a Hittite.'
Source: Dialogue with Trypho (New Advent)