It is an ill bird that fouls its own nest

Russian translation

Только дурная птица пачкает собственное гнездо.

Только недостойный человек дурно отзывается о собственной семье, доме, коллективе или наносит им ущерб.

Derivation

To foul one's own nest.

Variation

It is an ill (foul) bird that defiles its own nest.

Synonyms

Don't tell tales out of school.

Comparison

Худая та птица, которая гнездо свое марает.

Не вынови из избы сору [так меньше будет вздору]

Examples

And where's the use o' vilifying one's country, and bringing a discredit on one's kin, before southrons and strangers? It's an ill bird that files its own nest. (W. Scott)

“You're English, then?” “Pure,” said Mr. Blythe. “So am I; so's old Foggart – I looked him up in the stud-book. It's lucky, because we shall certainly be assailed for lack of patriotism.” “We are,” said Mr. Blythe. “People who can see no good in their own country... Birds who foul their own nest.” (Galsworthy)

It seemed to me as I lay tossing that Cordelia had not only fouled her nest but the universe, that the very war was hardly worth winning if she was what our boys would come home to. (Auchincloss)