The source of this very famous anecdote is the 14th century account by Gabriel de’ Mussi’s (de Mussis'), but Barker has just disputed the trustworthiness of the account.

You can find the reference to relevant primary text (in translation) as well as a few recent secondary literature in the notes of her article.

Reference:

• (Now Open Access): Barker, Hannah. "Laying the Corpses to Rest: Grain, Embargoes, and Yersinia pestis in the Black Sea, 1346–48." Speculum 96:1 (2021): 97-126. https://www.journals.uchicago.edu/doi/full/10.1086/711596