Genesis 6:19

19 And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female.

Genesis 7:2

2 Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.

This one pops up with surprising regularity. God said 2 of each in chapter 6, then tells Noah to bring 7 of the clean beasts in chapter 7.

Genesis 7:2 reiterates the command given in Genesis 6:19, and tells us that it was specifically for the unclean animals. More details in another account does not mean there is a contradiction. If you take 7 clean animals, you also take 2 clean animals.