In the begining when Cain kills Abel, then runs off and weds a wife. Where does the wife come from? There were only Adam, Eve, Cain and Abel…there was not mention of a woman other than Eve.

Answer:

God gave them a command to go forth and multiply and fill the earth.

As you study the Bible, it is evident it does not always include accounts of all lines of lineage and children born, only those who were part of the lineage of Christ, or needed to be included for another purpose. The Bible included telling us specifically about Cain, Abel, Seth, etc but does not go into detail on the hundreds of children Adam and Eve no doubt had. They lived to be very, very old as did all the people of this time so they could populate the earth…

Genesis 5:3 And Adam lived an hundred and thirty years, and begat a son in his own likeness, after his image; and called his name Seth:

So, to answer your question. They married their cousins, second cousins, perhaps even sisters at times. It was not uncommon at all for this to happen at this time, and there was no law against it. We even read in the Bible about accounts where brothers took the other’s wives if one of them died so that children could continue to be born since this was God’s command.

I hope this helps,
Pastor Brad