What is the ruling on saying: "O Messenger of Allah, rescue us"?

The statement "O Messenger of Allah, protect us" is a supplication to the Messenger of Allah, may Allah bless him and grant him peace, asking him to shield and protect the supplicant. Since supplication is an act of worship, and the Qur'an, Sunnah, and consensus have established the prohibition of supplicating anyone other than Allah, this act is polytheism (shirk), which Allah does not forgive. Therefore, whoever commits this act is an infidel.