There are of course a number of quotes of significance in both the Tale and the Prologue, and I encourage you in particular to not examine them separately but to see them as partner texts and consider how one casts light on the other and vice versa. However, for me, the central kernel of truth in this amazing text has to come from the Tale itself, when the knight, facing an impossible decision of either having a wife who is beautiful but unfaithful or ugly but faithful, decides to leave the choice up to his wife, giving her the "mastery" that she and all women desire:
My lady and my love, my dear wife too,
I place myself in your wise governance;
Choose for yourself whichever's the most pleasant,
Most honourable to you, and me also.
All's one to me; choose either of the two;
What pleases you is good enough for me.
This of course is the answer to the question that is posed by the Wife of Bath in her Prologue, when she asks what it is that women really desire. The way in which the young knight gets both a beautiful and a faithful wife because he gives his wife mastery over him cements the Wife of Bath's point: a wife's possession of mastery is what is best for both men and women, according to the Wife of Bath.