How does Chaucer's "Prologue to The Wife of Bath's Tale" from The Canterbury Tales compare to a tale from The Decameron?
While there are several tales from The Decameron that make repeat appearances in The Canterbury Tales, as retelling of old tales was the norm during early periods of literary history, there is none that is critically identified as a match for Chaucer's "The Wife of Bath's Prologue." To illustrate this point, critics recognize The Decameron, "Eighth Day, Novel I" as retold in Chaucer’s "The Shipman's Tale" and "Ninth Day, Novel VI" as a story retold in his "The Reeve's Tale."
Having said this, "Eighth Day, Novel 7" has some similarity to part of the Wife's Prologue in that both tell the story of a scholar who loves a widow, but they treat each other wickedly.
 Such then were the consequences of her flouts to this foolish young woman, who deemed that she might trifle with a scholar with the like impunity as with others .... (The Decameron, VIII, 7)
It was the Wife's fifth husband who was the scholar, and it was over a book that the punishments began, but this is really as far as the similarity extends:
717 But now to purpos, why I tolde thee
That I was beten for a book, pardee.
Upon a nyght Jankyn, that was oure sire,
720 Redde on his book as he sat by the fire
Of Eva first, that for hir wikkednesse (The Canterbury Tales, “The Wife of Bath's Prologue”)
In addition to this, though, "Seventh Day, Novel XI" is recognized as similar to the "Wife of Bath's Tale" in that both are tales of a test of love. Boccaccio's tale is borrowed from two earlier folk tales that he combined to make his version. Chaucer borrowed the themes of a test of love and illusion to create his tale. In Boccacio's, a wife's lover asks her to perform three tests of her love. She does so, then taunts her husband by entertaining her lover right in his presence and convincing him he sees an illusion. Though this tale perhaps has more in common with "The Merchant's Tale" as the scenes of the infamy in the tree branches are essentially the same.
"Foul fall thee, if thou knowest so little of me as to suppose that, if I were minded to do thee such foul dishonour as thou sayst thou didst see me do, I would come hither to do it before thine eyes!  (The Decameron, VII, 9)
Yet there is a decided parallel with the Wife's Tale in that (1) the hag asks the knight for a test of love through marriage and (2) the power of magical illusion makes the knight see one thing when another thing is true.
1225 "Two choices," said she, "which one will you try,
To have me foul and old until I die,
And be to you a true and humble wife,
And never anger you in all my life;
Or else to have me young and very fair
1230 And take your chance with those who will repair
Unto your house, and all because of me,
Or in some other place, as well may be.
Now choose which you like better and reply." (The Canterbury Tales, "The Wife of Bath's Tale")