References that dealt with the story of Moses peace be upon him, tell that he was heavy-tongued with a blemish that prevented him from pronouncing some letters correctly because of eating a small ember burned his tongue, when Pharaoh wanted to test him. His story became popular and spread until it becomes an axiom, although the scholars agree that the Prophets (peace be upon them) are infallible from the defects that prevent them from delivering the religion, and from every defect alienates people from them. So, I have dealt with this story by researching and studying, to know the source, and scholar's opinions, discern after searching and analyzing that it's from Israeli Stories which leak to our Islamic resources, contributed to it is spread scholar's correction that's referred to Ibn Abbas-may Allah be pleased him-they were not able differentiate between what's referred to him, and what's referred to the messenger of Allah.
Al-Qudah, Yahya Mahmoud
"The Story of the Knot of Musa's Tongue, Peace be upon him - A Critical Study,"
Jordan Journal of Islamic Studies: Vol. 14
, Article 14.
Available at: https://digitalcommons.aaru.edu.jo/jois/vol14/iss4/14