This is an excerpt from a Q & A session of the great scholar Shaykh Muhammad Uthaymeen رحمه الله
Is it permissible for a woman to request a divorce from her husband if he wishes to marry a second wife? And this is due to her not being able to stay with him? She says, she has much self-esteem and is unable to remain with him. Therefore is she sinful and what is the ruling concerning this?
Shaikh Uthaymeen رحمه الله answers:
Certainly what is befitting is for this woman to assist her husband in (acquiring) the mahr (dowry) for the second wife. Because this is what should be done. For indeed polygyny, if the man is confident within himself, in being just; and is confident within himself in being physically capable; and is confident within himself being financially capable, (then polygyny) is something desirable.
We encourage the young men to marry more than one woman: One, two, three, four; and if Allah brings (to us) female servants, we say, take from the female slaves whatsoever you desire. So that the children and offspring of the Muslim nation increase in number.
Since the Messenger ﷺ said:
” تَزَوَّجُوا الْوَدُودَ الْوَلُودَ فَإِنِّي مُكَاثِرٌ بِكُمُ الأُمَمَ ”
“Marry women who are loving and very prolific, for I shall outnumber the peoples by you..” [Sunan Abi Dawud 2050]
Therefore, my counsel to this sister who is asking is to assist her husband in what he is seeking, and if she possesses some wealth, then let her assist him with her wealth. And let her accustom herself to being patient and anticipate her reward from Allah. And it may that after he consummates the marriage that the matter becomes easier on her.
Though, they mention that if a person marries a second wife along with the first, her heart, (i.e., the first wife) becomes jealous. However, if he marries a third along with the other two then this jealousy vanishes. Hence, at that time, we have a treatment (i.e., for the jealousy), which is to marry a third woman!
I mention this, not as a joke, but from seriousness as this is a reality. That the woman becomes jealous if she has one co-wife, and her jealousy subsides if there is a third co-wife.
How is that?
She says, as long as there is a co-wife for my co-wife, who has come to me and made things miserable (as she claims), this lessens (the adversity). This is because the participation of others in your affliction takes away from (the gravity of) affliction upon you.
For this reason, Allah mentions:
وَلَن يَنفَعَكُمُ ٱلْيَوْمَ إِذ ظَّلَمْتُمْ أَنَّكُمْ فِى ٱلْعَذَابِ مُشْتَرِكُونَ
And never will it benefit you that Day, when you have wronged, that you are [all] sharing in the punishment. [Surah az-Zukhruf (Ornaments) 43 : 39]
Yet in the Dunya, if (some) criminals were to share in (receiving) a punishment, this would lessen (the adversity).