TT #264 · Parshas Shemini · Aliyah 7 · Passuk 47
Chabad.org — Vayikra Chapter 11 with Rashi
English: To distinguish between the impure and the pure, and between the animal that may be eaten and the animal that may not be eaten.
Shevuot 18b.
E-Daf.com — Shevuot 18b (Tsurras Hadaf)
English: Rabbi Chiyya bar Abba said in the name of Rabbi Yochanan: Whoever separates from his wife close to the onset of her menstrual period will have male children, as it is written, “to distinguish between the impure and the pure,” followed immediately by “when a woman conceives and bears a son.”
Textual linkage — the juxtaposition of the verse with the following verse supplies the homiletic connection.
Distinguishing impurity and purity is linked homiletically to this separation.