Charles Ellicott Commentary 2 Kings 21:10

"And Jehovah spake by his servants the prophets, saying," — 2 Kings 21:10 (ASV)

By His servants the prophets ... —This general expression is used because the historian found no name assigned in his source. It is possible that Isaiah was still living under Manasseh and protested in the manner here described against his apostasy.

More probably, however, the protests in question were those of that great prophet’s disciples: the style is not Isaiah’s. 2 Chronicles 33:18 refers to the history of the kings of Israel for “the words of the seers who spake to Manasseh”; and the originality of the language in 2 Kings 21:13 might be held to favor the view that in 2 Kings 21:11–15, we have an extract from that work embodying the authentic oracle of a contemporary prophet. (So Ewald.)

But it appears much more likely that the passage before us is a sort of résumé of the substance of many such prophetic addresses.