Commentary on Tafsir al-Jalalayn: ((Say, "Indeed, I have been commanded to worship Allah, [being] sincere to Him in religion")) regarding shirk (associating partners with Allah).

And His saying: He said: "regarding shirk (associating partners with Allah)" The intended meaning of religion here is the action that a person performs to be judged by it. Note the detail: the action he performs for the sake of being judged by it. As for an action where he does not expect to be judged by it, this is not called religion, even if it is an action. It must be that the doer acts in order to be judged by this action. Yes, He the Exalted says: And it has been passed to us many times that religion is used for the action and for the reward. So in His saying, the Exalted: it is the reward, and in His saying: it is the action.