Old proverbe says,
That byrd ys not honest
That fyleth hys owne nest.
Poems against Sir Christopher Garnesche, probably published c. 1523, reported in Bartlett's Familiar Quotations, 10th ed. (1919). Compare: "It is a foule byrd that fyleth his owne nest", John Heywood, Proverbs (1546) part ii. chap. v.