Leviticus 18:17
Leviticus 20:14
Oddly specific prohibition
If a man marries both a adult widow or divorced woman and her adult daughter then that is not the same as marrying his biological adult daughter and he might not be marrying a bioligical relative but for some reason it is forbidden to marry both a adult woman and her adult daughter in the old testament but not simply directly stated not to be married to more than one woman at a time