Polygamy in Islam

n seventh-century Arabia, when a man could have as many wives as he chose,
to prescribe only four was a limitation, not a license to new oppression. Further,
the Quran immediately follows the verses giving Muslims the right to take four
wives with a qualification which has been taken very seriously. Unless a man
is confident that he can be scrupulously fair to all his wives, he must remain
monogamous. Muslim law has built on this: a man must spend absolutely the same
amount of time with each of his wives; besides treating each wife equally financially
and legally, a man must not have the slightest preference for one but must
esteem and love them all equally. It has been widely agreed in the Islamic
world that mere human beings cannot fulfill this Quranic requirement: it is
impossible to show such impartiality and as a result Muhammad's qualification,
which he need not have made, means no Muslim should really have more than one
wife. In countries where polygamy has been forbidden, the authorities have
justified this innovation not on secular but on religious grounds.

Karen Armstrong, Muhammad: A Biography Of The Prophet
-- p. 191

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With regard to polygamy, Muhammad did not introduce this practice, as has
so often been wrongly alleged. The Scriptures and the other sacred books bear
abundant proof of the fact that is was recognized as lawful and, indeed, widely
practised by patriarchal prophets, Zoroastrians, Hindus and Jews. In Arabia
and all the surrounding countries a system of temporary marriages, marriages
of convenience, and unrestricted concubinage was also prevalent: this, together
with polygamy, had most disastrous effects on the entire moral and social structure,
which Muhammad remedied.

Muhammad married Khadija at the age of 25, and he took no other wife during
the twenty-six years of their married life. He married Aisha . . . at the age
of 54, three years after the death of Khadija. After this marriage, he took
other wives, about whom non-Muslim writers have directed much unjust criticism
against him. The facts are all these ladies were old maids or widows left destitute
and without protection during the repeated wars of persecution, and as head
of the State at Medina the only proper way, according to the Arab code, in
which Muhammad could extend both protection and maintenance to them was by
marriage. The only young person was Maria the Copt, who was presented to him
as a captive of war, and whom he immediately liberated, but she refused to
leave his kind protection and he therefore married her.

. . . 'Ye may marry of the women who seem good to you two or three or four,
but if ye fear that ye cannot observe equity between them, then espouse but
a single wife' (iv.3) . . . the growing majority of Muslims interpret the above
verse as a clear direction towards monogamy . . . -- p. 41-43

Sir Abdullah Suhrawardy, The Sayings of Muhammad