Parashas Metzora · Passuk 15:18
Chabad.org — English translation + Rashi
Torah Temima points to Niddah 32a.
English: “And a woman” — I have only an adult woman; from where [do we include] a girl of three years and one day for bi’ah? Scripture teaches “and a woman.”
Age threshold for female impurity from bi’ah
Chazal include a girl from three years and one day in the impurity consequences of this verse.