it is a wise child that knows his own father

The expression itself is ancient, attested in Homer’s Odyssey: “μήτηρ μέν τέ μέ φησι τοῦ ἔμμεναι, αὐτὰρ ἐγώ γε οὐκ οἶδ’· οὐ γάρ πώ τις ἑὸν γόνον αὐτὸς ἀνέγνω”. A version, “it is a wise father that knows his own child” (spelling modernized), is used in William Shakespeare’s The Merchant of Venice, and the modern version, in a translation of the Odyssey by Samuel Butler (see quotations), which likely popularized the proverb.

来源：wiktionary