Is it permissible to swear by "wal-Nabi" (by the Prophet) to affirm something?

Swearing by other than Allah, including swearing by the Prophet (peace be upon him), is forbidden and is a type of shirk (polytheism); because swearing is a form of glorification of that by which one swears, and a creature does not glorify another creature with the glorification of worship. This is indicated by the saying of the Prophet (peace be upon him): "Whoever swears by other than Allah has disbelieved or committed shirk," and "Whoever has to swear, let him swear by Allah or keep silent." As for Allah Almighty swearing by His creations in the Quran, that is specific to Him, Glorified be He. He has the right to swear by whatever He wills, but a creature should only swear by his Lord.