There isn’t a single commandment sanctioning it. There are ones about not multiplying wives to oneself, though.
Something is not automatically “biblical” by virtue of being mentioned in the Bible. By that logic, people might think that what Jephthah did to his daughter was acceptable to God when it was not.
honor thy mother and father.
not
father and father
not
mother and mother
not father and mother and mother and mother and mother and mother and mother
not
hippie comune.
I was in a rush when I posted. What I should have said was, "at least polygamy is not an abomination"