TT #304 · Parshas Tazria · Aliyah 7 · Passuk 58
English: The garment, warp or woof, or any leather article that you wash, if the lesion disappears from it, shall be washed a second time and be clean.
Torah Temimah cites Chullin 31b for requiring both washings to be intentional.
E-Daf — Chullin 31b · Shas.org · Sefaria — Chullin 31b, source text and translation
English: Just as the first washing must be intentional, so must the second washing.
Textual derivation
Both the first and second washings must be intentional acts.