Answer
Wa `alaykum as-Salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- Marriage in Islam has some conditions. As long as these conditions are fulfilled, the marriage is valid.
2- As for the second marriage, it is not a must to take the permission of the first wife except if this was stipulated in the marriage contract or promised by the husband.
3- The husband is highly recommended to consider the feelings and emotions of his first wife.
4- One should not violate the laws of the countries they live in, travel or migrate to, or pass by.
In his response to your question, Dr. Wael Shehab, PhD in Islamic Studies from Al-Azhar University, and currently the Imam of the Downtown Toronto Masjid in Canada, states:
First of all, it should be clear that a valid marriage in Islam should meet some requirements, among which are-
1- presence of witnesses;
2- publicity of the marriage (ish-har);
3- payment of the dower to the wife;
4- consent of both parties (the husband and the wife), and
5- the acceptance of the wife’s walli (guardian).
As for the first wife’s agreement to a second marriage, the husband should seek his first wife’s agreement if it is stipulated in the marriage contract that the husband should not take a second wife without the first wife’s approval.
Also, if the husband has promised his wife not to take a second wife without her permission, he has to respect his word.
However, if the marriage contract does not have such a condition and the husband has not promised his first wife to tell her if he takes a second wife, then he is recommended to wisely and kindly consider her feelings and emotions.
He should avoid harming her feelings and should properly approach her out of goodness and well-treatment to one’s wife, which is highly encouraged in Islam.
Though taking a first wife’s permission is not a condition for the validity of a second marriage in this situation, considering her feelings and emotions is highly recommended.
Finally, it should be clear that a Muslim is not allowed to violate the laws of marriage of the countries they live in, travel or migrate to, or pass by.
Allah Almighty knows best.