“I will not ask.” This sounds very holy, but actually Ahaz was hoping to deceive Isaiah. Ahaz did not think he needed a sign from Yahweh that Syria and Israel would be defeated in a war because he had already taken the gold and silver from the Temple and hired Tiglath Pileser, the king of Assyria, to attack Syria and Israel. Tiglath Pileser attacked and conquered Syria in 732 BC, during the reign of Pekah of Israel and Ahaz of Judah. Later, after the reign of Pekah and during the reign of Hoshea, the Assyrian king Shalmanezzar, who succeeded Tiglath Peleser, conquered Israel and deported the people about 722 BC.
But God knew of Ahaz’s attempted deception and his plot to hire the Assyrians, as we see in Isaiah 7:13, and God gave Ahaz a sign of victory anyway (Isa. 7:14-16).