Is the letter sold in the lands of the Haram, claimed to be the letter of the Prophet, peace and blessings be upon him, to Al-Mundhir ibn Sawa, written in his noble hand, authentic?

This letter is not in the handwriting of the Prophet, peace and blessings be upon him, because he was illiterate and could not write, as indicated by the noble verse: {And you did not recite any book before it, nor did you inscribe it with your right hand.} [29:48] It has been proven that the Prophet, peace and blessings be upon him, had scribes who wrote down the revelation and letters. Some contemporary scholars have mentioned that this letter is in the handwriting of Ubayy ibn Ka'b, may Allah be pleased with him.