All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Custody of the disabled child is amongst the acts that are most pleasing to Allah the Almighty because it is all about caring for the weak, feeling compassion for him, and helping him overcome his affliction. The Prophet, peace and blessings be upon him, said, “The most beloved people to Allah are those who are most beneficial to the people." {Related by Tabarani, vol.12/pp.453}. In addition, the reward for taking care of a disabled child may even be greater than taking care of an orphan because it involves a great deal of hardship on the part of the person performing this task.
Accordingly, We (Iftaa` Department) advise the above mother-whom Allah has tested with this child-to accept Allah`s Decree and Destiney and never abandon her child for he is part of her, and he may be a reason for her happiness in this life and salvation in the Hereafter. It might be that Allah Has Tested her with this child to raise her in rank. If she exercises patience and takes care of him hoping for reward from Allah, Allah Might Advance her reward by blessing her with righteous and healthy children.
However, if she insisted on not taking custody of her child, then she can`t be forced to that. This is because the majority of the Muslim scholars stated that custody of child is the right of the mother and she can`t be forced to it unless the child doesn`t accept to be breastfed but from her or the father can`t afford child-care services.
Ibn Hajar (May Allah be pleased with him) says: "The mother can`t be forced to take custody of child because she isn`t obligated to spend on him/her." {Tohfat Al-Mohtaaj, vol.8/pp.359}.
Moreover, Al-Bahooti, a Hanbanli scholars, says: "Even if the mother refrained from child custody, she can`t be forced to it because it isn`t obligatory upon her." [Khash-Shaaf Al-Khinaa`, vol.5/pp.496].
Ibn Abdeen (May his soul rest in peace) says: "Scholars have differed as regards the ruling on child custody: Is it a right of the mother/female custodian or the child?
Regarding the first view, If she refrained from custody then she can`t be forced to take it. This view was outweighed by a number of scholars and it is my view (Ibn Abdeen).
Regarding the second view, she is forced to custody, as decided by the three scholars: Abu Al-Laith, Al-Hindawi, and Jawahir Zadah….." {Raad Al-Mohtaar, vol.3/pp. 559-560}.
That being said: "if the mother is able to take care of her disabled child but didn`t, then We hope that, with the passage of time, her heart will soften and that she shows affection to him." Either way, this issue shouldn`t be a reason for separation between these spouses. And Allah the Almighty Knows Best.