1 Samuel 1:2-7
And he had two wives; the name of the one was Hannah, and the name of the other Peninnah: and Peninnah had children…
There can have been no polygamy when as yet there was only a single pair, or when there were several single pairs widely separated from each other. The presumption, if not the certainty, therefore, is that primeval man must have been monogamous. It is a presumption supported by the general equality of the sexes in respect to the numbers born, with only just such an excess of the male sex as tends to maintain that equality against the greater risks to life arising out of manly pursuits and duties. Thus the facts of Nature point to polygamy as in all probability a departure from the habits of primeval times.
(Argyll, Unity of Nature.)
Parallel VersesKJV: And he had two wives; the name of the one was Hannah, and the name of the other Peninnah: and Peninnah had children, but Hannah had no children.