The Ruling on Swearing by the Messenger (peace and blessings be upon him)

Question : But if someone says, "By the Messenger of Allah," and swears by the Messenger (peace and blessings be upon him), is this permissible?

Answer : Is it permissible to swear by the Messenger? If someone says to you, "The Messenger (peace and blessings be upon him) is the greatest of creation, the greatest of creation, so why is it not permissible to swear by him?" The answer is that the greatest of creation is the One who said, "Whoever swears by other than Allah has committed disbelief or shirk (associating partners with Allah)." Therefore, swearing by the Prophet is shirk. If a person says that some people have this oath on their tongues, meaning they say, "By the Prophet."