Leviticus 12:5

But if she bear a maid child, then she shall be unclean two weeks, as in her separation: and she shall continue in the blood of her purifying threescore and six days.

Cross-reference

Leviticus 12:2 introduces the purification law for a male child, which this verse for a female child parallels with longer days.

Leviticus 12:4 specifies the purification for a male child; this verse for a female child directly extends that rule with doubled time.