of their ever committing shirk: indeed, it is altogether impossible, for they had already passed away, and the prophets are divinely protected from associating partners with Him.

He—exalted is He—also says:
“Say, ‘Is it other than Allah that you command me to worship, you ignorant ones? It has already been revealed to you and to those before you that, if you commit shirk, all your deeds will surely be nullified and you will certainly be among the losers. Rather, worship Allah alone and be among the grateful.’” ⦗al-Zumar: 64–66⦘

This address is directed to everyone. Here the particle inna is used because the speech is aimed at those who are alive, whereas the earlier passage was information about those who had died. The same principle applies to His words:

“If you are in doubt about what We have sent down to you, then ask…” ⦗Yunus: 94⦘.

The verse does not imply that any doubt actually occurred, nor that any question was ever posed. Rather, the Prophet—may Allah bless him and grant him peace—was never in doubt and never asked any of them. It is even related that he said, “By Allah, I neither doubt nor ask.”