Giving zakaah to one’s mother if her husband does not spend on her
Question

                There is a man who does not give his wife her rights with regard to maintenance, and he does not spend on her properly. Can her son give her something from the zakaah on his wealth to suffice her?.
Praise be to Allah.It is not permissible to 
    give one’s mother zakaah that is the share of the poor and needy, because 
    spending on her is obligatory upon her husband; if he is poor or refuses to 
    spend on her, then her children must spend on her. 
Ibn Qudaamah (may Allah 
    have mercy on him) said in al-Mughni (2/279): If the poor woman has a 
    husband who is well off, he should spend on her and it is not permissible to 
    give zakaah to her, because she will have what is sufficient for her by 
    means of what reaches her of that obligatory maintenance. If he does not 
    spend on her and is unable to do so, it is permissible to give (zakaah) to 
    her. This was stated by Ahmad. 
End quote. For more 
    information please see the answer to question no.
    102755 
If she does not have proper 
    maintenance because her husband is poor or miserly, then her children are 
    obliged to spend on her enough to suffice her, if they are able to do so. 
Ibn Qudaamah (may Allah 
    have mercy on him) said in al-Mughni, 2/269: Nothing of the 
    obligatory charity (zakaah) should be given to one’s parents or children. 
    Ibn al-Mundhir said: The scholars are unanimously agreed that it is not 
    permissible to give zakaah to one’s parents when the one who is responsible 
    for their maintenance is obliged to spend on them, and giving zakaah to them 
    will mean that they no longer need this maintenance, in which case 
    maintenance would be waived in such as way that he will benefit from that, 
    and it is as if he gave the zakaah to himself.
End quote. 
But if they are not able to 
    spend on her, then it is permissible to give zakaah to her, because it is 
    not obligatory for them to spend on her in that case. 
Shaykh al-Islam Ibn 
    Taymiyyah (may Allah have mercy on him) said: It is permissible to give 
    zakaah to one’s parents and grandparents, no matter how far the line of 
    ascent reaches, and to one’s children and grandchildren, no matter how far 
    the line of descent reaches, if they are poor and he is unable to spend on 
    their maintenance.
End quote from Majmoo‘ 
    al-Fataawa, 5/373. See also: ash-Sharh al-Mumti‘, 6/92; and the 
    answer to question no. 85088 
It is also permissible to 
    give zakaah to the mother under a category other than that of the poor and 
    needy, such as debtors, because it is not obligatory for him to pay off his 
    mother’s debt, so it is permissible to give her zakaah in order to pay off 
    her debts with it; rather she is more entitled to that. For more details 
    please see the answer to question no.
    39175. 
And Allah knows best.