True is, that whilome that good poet sayd,
The gentle minde by gentle deeds is knowne:
For a man by nothing is so well bewrayd,
As by his manners.

Edmund Spenser (c. 1552-1599) English poet

The Faerie Queene, Book 6, Canto 3, st. 1 (1589-96)
    (Source)

Spender is referencing Chaucer's "Wife of Bath's Tale" in the Canterbury Tales: "he is gentil that doth gentil dedis."