Genesis 16:3

Ten years after she was 65; which shews that she might reasonably conclude she would now have no children herself; and as she knew God had promised Abram a son, she thought he might follow the custom of those times, and have him by a second wife. Abram shewed no eagerness on this matter, but only yielded to his wife's petition, deprecanti, being well aware of the inconveniences of polygamy, which Sarai had soon reason to observe. This is the first time we read of polygamy since the deluge; but it is not mentioned as any thing singular or unlawful. This was a matter in which God could dispense; but it was never left to the disposal of any man. Hence, when Luther and his associates ventured to dispense with the Landgrave of Hesse, to keep two wives at once, he required him to keep it a secret, being ashamed of his own conduct. He still maintained it was a thing indifferent, even in the law of grace, though Christ has so expressly condemned it. See præp 62, 65. The practice, so common of late in this country, of marrying again after a bill of divorce has been passed, is no less contrary to the Catholic doctrine, which allows only a separation of the parties from bed and board, in cases of adultery; but never of a second marriage, while both the parties are living. (1 Corinthians vii.; St. Augustine de Adult. Conj. i., City of God xvi. 25, 38; and other fathers.) (Haydock)

It was never lawful for one woman to have two husbands. (Worthington)

To wife. Plurality of wives, though contrary to the primitive institution of marriage, Genesis ii. 24, was by Divine dispensation allowed to the patriarchs; which allowance seems to have continued during the time of the law of Moses. But Christ our Lord reduced marriage to its primitive institution, St. Matthew xix.