Can he give his zakaah to his married daughter who is poor as her husband is missing?

If a woman is married, then her maintenance is obligatory on her husband. If he is poor or is absent and has not left her any money to cover her maintenance, and she is poor and has no money, it is permissible to her to be given zakaah. 

Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (2/279): If a poor woman has a husband who is well off and spends on her, it is not permissible to give zakaah to her, because she has sufficient income from what she receives of obligatory maintenance. But if he does not spend on her and it is not possible to make him do so, then it is permissible to give zakaah to her. This was stated by Imam Ahmad. End quote. 

But her mother or father are not allowed to give her zakaah, because he (the father) is obliged to spend on her in this case, except in two situations: 

1.Giving her zakaah in order to pay off her debts which she borrowed for something other than maintenance.

2.If the father is unable to spend on her, but he has wealth on which zakaah is due, in which case it is permissible for him to give her his zakaah.

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked: is it permissible to give zakaah to a married daughter who is in need? 

He replied: in every case where a person meets the description of those who are entitled to zakaah, the basic principle is that it is permissible to give zakaah to him. Based on that, if a man is not able to spend on his daughter and her children, he may give zakaah to her. But it is better and more on the safe side to give it to her husband. End quote. 

He was also asked: is it permissible to give my zakaah to my married daughters, knowing that they are poor? 

He replied: the scholars stated that a man should not give zakaah to his offspring or to his father and grandfather or to his mother and grandmother, in other words not to his ascendants or descendants. This applies if it is given in order to meet their needs. But if they have debts and it is not given as maintenance, then it is permissible to give it to them, because he is not obliged to pay off their debts and hence giving his zakaah to them is not regarded as a way to save money. 

To sum up the answer: with regard to this man who has married daughters whose husbands are poor, if he does not have sufficient wealth to spend on them, then there is nothing wrong with giving his zakaah to them, but he may give the money to the husbands, because they are the ones who are responsible for maintenance. So there is nothing wrong with that whatever the case. End quote. 

Majmoo’ Fataawa Ibn ‘Uthaymeen (18/426) 

And Allaah knows best.