[FNU LNU]

and how do we know that Mary Magdalene was a prostitute?

[Bohemund]

and how do we know that Mary Magdalene was a prostitute?

We don't, of course. Pope Gregory the Great conflated three different women into "Mary Magdalene," confusing the sinner of Luke 7:35-50 with Mary, sister of Martha and Lazarus with Mary Magdalene.