Surah An-Nisaa (4) — Ayah 129

129. You will never be able to deal justly between your wives, even if you desire to do so [171]. So do not incline completely toward one, leaving the other hanging [172]. But if you make amends and are mindful of Allah, then surely Allah is Most Forgiving, Most Merciful.

[171]
Reasons for Inclination Towards One Wife:

This is because, for example, one wife is young, the other is old; one is beautiful, the other is of average appearance or unattractive; one is a virgin, the other is previously married; one is good-natured, the other is ill-tempered; one is intelligent and clever, the other is dull and slow-witted. Now, it is obvious that these are such qualities in which, although the woman herself has no role, they certainly become a cause for the husband's inclination or lack thereof, and this is a natural matter. Over such inclinations or lack thereof, a person has no control, therefore there is no accountability or reproach from Allah for such matters. Accountability will only be for those things which are within a person's control, such as providing maintenance and other necessities of life, assigning turns to the wives, etc. Now, regarding those matters which are not within a person's power, about them Allah Almighty has said that you will not be able to do justice as is due.

[172]
The Reality of Justice Between Wives:

That is, in those matters in which a person has the ability to be just, those must certainly be observed. From this, it will automatically result that you will neither incline completely towards only one wife, nor will you be able to remain completely detached from another. In the explanation of this verse, consider the following hadiths:
1. The Prophet ﷺ said, "Whoever has two wives and inclines towards one of them, he will come on the Day of Resurrection with one of his sides drooping."
[دارمی، کتاب النکاح، باب فی العدل بین النساء]
2. Sayyida Sawda bint Zam'a ؓ gave her turn (and in one narration, her day and night) to Sayyida Aisha ؓ. In this way, the Prophet ﷺ used to stay with Sayyida Aisha ؓ for two days, one being her own turn and one being Sawda's ؓ turn.
[بخاری، کتاب النکاح باب المراۃ تھب یومھا من زوجہا لضر تھا و کیف یقسم ذلک]
3. Sayyida Aisha ؓ narrates that it was the Prophet's ﷺ practice that after Asr, he would visit all his wives.
[بخاری، کتاب النکاح، باب دخول الرجل علی نساۂٖ فی الیوم]
4. Sayyida Aisha ؓ narrates that when the Prophet ﷺ became ill (in his final illness) and the illness intensified, he sought permission from the other wives for his care to be done in her house, so all the wives gave him permission.
[بخاری، کتاب الہبہ، باب ھبۃ الرجل لامرأتِہٖ و المراۃ لزوجھا]
5.
Refutation of the Theory of Monogamy:

Sayyiduna Anas ؓ narrates that it is Sunnah that when one marries a virgin, he should stay with her for seven days and then assign turns. And when he marries a previously married woman, he should stay with her for three days and then assign turns.
[بخاری کتاب النکاح، باب اذاتزوج البکر علی الثیب و باب اذاتزوج الثیب علی البکر]
Some Muslims, who are impressed by Western civilization and are proponents of monogamy, object that Islam, on one hand, permits polygamy, but on the other hand, by declaring justice impossible, practically cancels this permission. One answer to this is that Allah Almighty has declared justice impossible only in those matters which are beyond human control, and there is no accountability for them, as mentioned above. The second answer is present within this very verse, in which Allah Almighty has said, "Therefore, do not incline completely towards only one wife." From this, it is clear that Allah has permitted more than one wife. In this way, their doubt or objection is completely refuted.