They say
A real prophet would never practice polygamy.
If polygamy means a man cannot be a prophet, start in Genesis. Abraham, Jacob, and Moses had more than one wife. 2 Samuel 12:8: the Lord says He gave David his master’s wives. Nathan rebuked David for murder and theft, not for having more than one wife. Their Bible already has this. They only treat it as disqualifying when Joseph did it.
Genesis 16:3
KJV · Sarai Abram’s wife took Hagar… and gave her to her husband Abram to be his wife.
NRSVUE · Sarai… took Hagar… and gave her to her husband Abram as a wife.
2 Samuel 12:8
KJV · I gave thee thy master’s house, and thy master’s wives into thy bosom.
NRSVUE · I gave you your master’s house and your master’s wives into your bosom.

