Genesis 7:2-3, 8-9

Take with you seven pairs, each male with its female, of every kind of clean animal, and take one pair, each male with its female, of every kind of unclean animal. Take seven pairs of all the birds of the sky, each male with its female. This will allow all these animals to continue living on the earth after the flood.

The clean animals, the unclean animals, the birds, and everything that crawls on the ground came to Noah. They went into the boat in groups of two, male and female, just as God had commanded Noah.