Leviticus 14:30
And he shall offer the one of the turtledoves, or of the young pigeons, such as he can get;
Cross-reference
Leviticus 12:8 prescribes the same turtledoves or pigeons for a woman after childbirth, mirroring the offering here for a cleansed leper—both use a poor person's offering.
Leviticus 15:14 tells a man with a discharge to bring turtledoves or pigeons, exactly as the leper does here—both are part of restoration offerings.
Leviticus 15:15 details the use of the birds as sin and burnt offerings for a discharge, identical to the procedure here for the leper.
In Luke 2:24, Mary offers the same pair of birds as the law requires for a poor person's purification, showing fulfillment of the Mosaic law.
In Numbers 6:11, the same two-bird offering (sin and burnt) is made for a Nazirite's impurity—a parallel purification ritual.