TT #288 · Parshas Tazria · Aliyah 7 · Passuk 54
English: The priest shall command that they wash the article in which the lesion is found, and he shall isolate it another seven days.
Torah Temimah cites Sifra (Toras Kohanim) for the area of garment that must be washed with the lesion.
Sifra — Vayikra 13, Midrash Sefer
English: Should they wash only the lesion, or the entire garment? The Sifra derives that they wash the affected part together with the surrounding garment.
Textual derivation
The laundering must cover the lesion and the fabric around it; it is neither limited to the exact discolored spot nor extended indiscriminately to the whole garment.