Leviticus 22:21, 23

Whoever offers a sacrifice of peace offerings to the LORD to fulfill a special vow to the LORD or as a freewill offering from the herd or from the flock, it must be perfect to be accepted; there shall be no blemish in it.

For a freewill offering you may offer either a bull or a lamb which has an overgrown or stunted member (deformity), but for [the payment of] a vow it will not be accepted.