TT #274 · Parshas Tazria · Aliyah 7 · Passuk 49
English: and the lesion is greenish or reddish in the garment, leather, warp or woof, or any leather article, it is a lesion of tzaraas and shall be shown to the priest.
Torah Temimah cites Sifra (Toras Kohanim) for the gris-sized minimum measure for garment tzaraas.
Sifra — Vayikra 13, Midrash Sefer
English: A garment-tzaraas lesion must meet the minimum measure of a gris.
Textual derivation
A garment-tzaraas lesion must reach the stated minimum measure, called a gris.