Here is a common Muslim complaint:

There is a contradiction found between Genesis 6:19, 22; 7:2-3.
In Genesis 6 it says two of ALL living creatures shall be brought into the Ark, which would include both clean and unclean, and that Noah did all as he was commanded by God. Then in Genesis 7 God changed his mind and commanded that there be seven pair of each animal. So I ask, does "two" of all creatures mean "seven pair" of all creatures?

Let's review the passages in question:

And of every living thing of all flesh, you shall bring two of every kind into the ark, to keep them alive with you; they shall be male and female.
— Genesis 6:19 NASB

Thus Noah did; according to all that God had commanded him, so he did.
— Genesis 6:22 NASB

You shall take with you of EVERY CLEAN ANIMAL BY SEVENS¹, a male and his female; and of the ANIMALS THAT ARE NOT CLEAN TWO, a male and his female; also of the birds of the sky, by sevens, male and female, to keep offspring alive on the face of all the earth.
— Genesis 7:2-3 NASB

For contrast I have listed a few other translations of Genesis 7:2-3.

Take with you seven pairs of every kind of clean animal, a male and its mate, and one pair of every kind of unclean animal, a male and its mate, and also seven pairs of every kind of bird, male and female, to keep their various kinds alive throughout the earth.
— Genesis 7:2-3 NIV

Take with you seven pairs—male and female—of each animal I have approved for eating and for sacrifice, and take one pair of each of the others. Also take seven pairs of every kind of bird. There must be a male and a female in each pair to ensure that all life will survive on the earth after the flood.
— Genesis 7:2-3 NLT

From all clean cattle thou shalt take to thee seven; seven male and female; and from cattle which are not clean, this two, male and female. Also of birds of the heavens, seven: seven male and female, to preserve alive seed upon the face of all the earth.
— Genesis 7:2-3 SLT

The solution to this apparent contradiction is actually very easy to resolve, and is was already mentioned in the NLT. Let's go ahead and break it down anyway. It takes two of one kind in order to reproduce: male and female. So that is the minimum that must be present after the flood in order to repropagate the species. This is what we see when we read Genesis 6:19.

In chapter 7, we see God giving Noah what on the surface may seem like an entirely new command that is divorced from the first one found in 6:19. However, that is not the case. This is not God "changing his mind" but rather, it is God giving expanded or more specific instructions to Noah.
• clean animals by seven (pairs)
• unclean animals by 2 (1 pair)

Some of you may be asking, "Why would God do that?" Why not just tell Noah the full command at the onset? We don't specifically know the "why" for that because the Bible does not tell us. However, we can know the reason behind the command being given. Which is what we will be examine next.

Here's a logic question, if there are fourteen animals are there also two animals? The answer is yes, because you cannot arrive at fourteen animals unless you first arrive at two animals. 

That reasoning brings us to the next logical thing to consider: Why more than the single male & female pair originally instructed? The answer to that question was mentioned in the NLT translation above, but it is also specifically revealed to us in the following verses:

Every beast, every creeping thing, and every bird, everything that moves on the earth, went out by their families from the ark. Then Noah built an altar to the Lord, and took of every clean animal and of every clean bird and offered burnt offerings on the altar.
— Genesis 8:19-20 NASB

So if we are being intellectually honest, we see that the concern Muslims bring up is NOT a contradiction. There is a logical and reasonable explanation for God to instruct Noah to have the extra clean animals and clean birds: burnt offerings for him and the rest of his family.

This complaint has been nullified.

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1 The phrase "by sevens" is referring to male and female pairs, in otherwords, fourteen animals and also fourteen birds.