Is saying, "O Allah, grant blessings and peace upon our Master Muhammad, my means have been exhausted, O Messenger of Allah," considered polytheism (shirk)?

This word is considered polytheism (shirk) because it is an appeal for help to the Messenger -peace be upon him- and a complaint of one's state to him. This implies that he hears the call of anyone who calls him from anywhere, responds to those who seek his help, and relieves their distress. The Messenger was unable to do this during his lifetime, so how could he do so after his death? He does not know the unseen, nor does he possess the power to harm or benefit himself or others.

Allah Almighty said: (Say, "I hold not for myself [the power of] benefit or harm, except what Allah wills. And if I knew the unseen, I could have acquired much wealth"), and He Almighty said: (And your Lord says, "Call upon Me; I will respond to you"), and He Almighty said: (And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me).

It is obligatory upon the servant to supplicate to none but Allah, to seek help from none but Him, to hope for none but Him, and to rely on none but Him. For Allah alone holds sovereignty, and in His hand is all good, and He is over all things competent. Knowledge of the unseen, relief of distress, hearing the supplications of those who call, and responding to them are characteristics exclusive to the Lord -Glorified and Exalted be He-. So, whoever attributes any of that to other than Him commits major polytheism.

Allah Almighty said: (Is He [not best] who responds to the desperate one when he calls upon Him and removes evil and makes you inheritors of the earth? Is there a deity with Allah? Little do you remember"), and He Almighty said: (Say, "None in the heavens and earth knows the unseen except Allah").

Allah is the one who forgives sins, relieves distress, and knows what is in the breasts. Therefore, the servant must seek none but his Lord in achieving these desires, for He is the Guardian of that and is capable of it.