I've notices that there seems to be conflicting opinions on the number of wives the prophet Mohammad (pbuh) had.

I've heard people say he had as much as 20 wives and I have heard people say he had just 6. In different Islamic books I've read conflicting numbers too.

I am quite confused because I thought all Muslims agreed he had 11 wives.

How many wives did he [i]really[/i] have?, and can anybody prove this by quoteing an authentic source?

And why was he allowed to have more then 4 wives?

I would be grateful if you could help me out on this one.

Thanks.