An-Nisa' - 4:129

وَلَن تَسْتَطِيعُواْ أَن تَعْدِلُواْ بَيْنَ النِّسَاء وَلَوْ حَرَصْتُمْ فَلاَ تَمِيلُواْ كُلَّ الْمَيْلِ فَتَذَرُوهَا كَالْمُعَلَّقَةِ وَإِن تُصْلِحُواْ وَتَتَّقُواْ فَإِنَّ اللّهَ كَانَ غَفُورًا رَّحِيمًا
[4:129]
And you have it not in your power to do justice between wives, even though you may wish (it), but be not disinclined (from one) with total disinclination, so that you leave her as it were in suspense; and if you effect a reconciliation and guard (against evil), then surely Allah is Forgiving, Merciful.
Ye are never able to be fair and just as between women, even if it is your ardent desire: But turn not away (from a woman) altogether, so as to leave her (as it were) hanging (in the air). If ye come to a friendly understanding, and practise self-restraint, Allah is Oft-forgiving, Most Merciful.
Ye will not be able to deal equally between (your) wives, however much ye wish (to do so). But turn not altogether away (from one), leaving her as in suspense. If ye do good and keep from evil, lo! Allah is ever Forgiving, Merciful.