From A Day in a Medieval City by Chaira Frugoni:
One day in Florence Dante had left the house after eating, and while passing through Porta San Pietro, came upon “a smith who was beating iron on the anvil and singing Dante the way one sings a popular poem, and mixing his verses up, shortening some and lengthening others, so that it seemed to Dante that he was receiving a great injury from the fellow.” Without a word Dante went into the man’s workshop and threw his tongs, his hammer, his balances, and all his other implements into the street. When the smith remonstrated loudly at finding himself stripped of the tools of his trade and blocked from exercising his own special skill, the poet replied, “‘You are singing from my work, but not the way I wrote it; I have no other art, and you are ruining it for me.’ The irate smith, at a loss for words, gathered up his things and went back to his work; and after that, when he wanted to sing, he sang of Tristan and Lancelot, and left Dante alone.”
On another occasion we meet the poet in Florence wearing a full suit of armor – which we might think unusual, but which was actually not out of place in the dangerous streets of the city: “And wearing armor to protect his throat and his arm, as people then customarily did,” the poet saw a donkey driver transporting garbage, “who was going along behind the donkeys singing the book of Dante, and when he had sung for a bit, he hit the donkey and said ‘Arri (Giddyup).’ Dante accosted him and dealt him a forceful blow on the shoulder with his mailed fist, saying, ‘I didn’t put that Arri in there.'” A lively dispute ensured, with bad language and obscene gestures on the part of the donkey driver, and insulting remarks on the part of Dante.
Both stories cite another book for origin, Franco Sacchetti’s Il Trecentonovelle (pgs 299-302).