"Like the custom [da'b] of the people of Noah, and 'Ad, and Thamud," the verse. Al-da'b means the habit/custom. The meaning is: I fear for you the like of the punishment [incurred by] their action, which is what Allah destroyed them with.

Muhammad said: "Al-da'b" according to the scholars of language means the habit. The meaning is: I fear for you that you will persist in your disbelief, and thus there will descend upon you from the punishment the like of what descended upon the past nations who denied their messengers; and this is what Yahya intended.