TT #251 · Parshas Shemini · Aliyah 7 · Passuk 43
Chabad.org — Vayikra Chapter 11 with Rashi
English: “Do not become impure through them”: a person who makes himself impure a little is caused to become impure much; impurity initiated below is met by impurity from above.
Yoma 39b.
E-Daf.com — Yoma 39b (Tsurras Hadaf)
Middah and consequence — The Chazal applies the verse’s wording and structure to establish the stated teaching.
One who begins to defile himself below is met with greater defilement from above.