Rashi on Deuteronomy 14:11/רש"י על דברים י״ד:י״א

1כל צפור טהרה תאכלו ALL CLEAN BIRDS YOU MAY EAT — 'All' — this is intended to permit as food also the bird that is set free in the case of a leper (i.e. at his purification rite; Leviticus 14:7) (Sifrei Devarim 103:1; Kiddushin 57a).