In fact, the Bible doesn’t specifically prohibit polygamy in the New Testament either.
Is their a NT verse that says “thou shalt not engage in polygamy?” or the equivilant?
No.
But can you read and comprehend what the NT does say when it references marriage? If you can, then you cannot in good faith state that one man, one woman marriage is untaught in the NT. It clearly is taught because when reference is made to God’s institution of marriage throughout the NT the context is that of a husband-wife, husband-wife, husband wife.
NOT husband-wives, husband-wives, husband-wives.
THere are many, but to me the most telling teaching in regard to the NT view of marriage is the teaching that Christ and his Church have the same spiritual relationship to one another that a husband and wife physically have to one another. The Church is represented spiritually as the Bride of Christ. Christ is represented as the Church’s husband. Christ is true to his bride, so much so that he gave up his own life on the Cross to save his church. And the church is to be faithful to her husband, Christ, or else it will become like an unfaithful wife is to her husband.
There are many other references all of which depict a husband and a wife, not a husband and wives.
Anyone who cannot learn from the context of biblical writings but believes you must have a verse that states in exact human wording what the prohibition is, does not understand the most simple concept relative to finding what the bible teaches on a subject.
The Old Testament:
May your fountain be blessed, and may you rejoice in the wife of your youth. --Proverbs 5:18
Has not [the LORD] made them one? In flesh and spirit they are his. And why one? Because he was seeking godly offspring. So guard yourself in your spirit, and do not break faith with the wife of your youth. -- Malachi 2:15
In the New Testament, one-man-one-woman marriage is distinctly Christian. Paul made marriage to one woman a necessity for role models in a church:
A deacon must be faithful to his wife and must manage his children and his household well. --Timothy 3:12