Read this and answer the question. If the question is unanswerable, say "unanswerable".

There are occasional brief hints and allusions in his longer works however that Avicenna considered philosophy as the only sensible way to distinguish real prophecy from illusion. He did not state this more clearly because of the political implications of such a theory, if prophecy could be questioned, and also because most of the time he was writing shorter works which concentrated on explaining his theories on philosophy and theology clearly, without digressing to consider epistemological matters which could only be properly considered by other philosophers.

Who wrote about distinguishing philosophy from prophecy?
unanswerable