Leviticus 13:35

אחרי טהרתו [AND IF THE SCALL SPREADS AT ALL …] AFTER HIS BEING PRONOUNCED CLEAN — I have here only the statement that he is unclean if it spreads after he has been freed from the quarantine; whence do I know that the same applies if it has spread by the end of the first week and or by the end of the second week? Because it states here: “if it spreads at all” (Sifra, Tazria Parashat Nega'im, Chapter 9 9).

וְאִם־פָּשֹׂ֥ה יִפְשֶׂ֛ה הַנֶּ֖תֶק בָּע֑וֹר אַחֲרֵ֖י טׇהֳרָתֽוֹ׃

But if the patch spread much in the skin after his cleansing;