Genesis 7:3

3Take seven pairs of every kind of bird, male and female together. Do this so that they will give birth to young ones. Then each different kind of animal and bird will continue to live on the earth.7:3 Clean animals are the kinds of animal that God accepted as a sacrifice. God told Noah to take more clean animals so that Noah could offer a sacrifice to God. There would still be animals that remained to give birth to young animals.