A wife giving up her right to maintenance; and is the first wife’s approval needed before one can marry a second wife?
Question

                Is it halal to have a second wife who says she does not need financial support. If so, what if the first wife does not allow the marriage..can a man still get married again?
Praise be to Allah.Maintenance 
          is one of the rights of the wife which is an obligation upon her husband. 
          Allaah says (interpretation of the meaning):  
“Men 
          are the protectors and maintainers of women, because Allaah has made 
          one of them to excel the other, and because they spend (to support them) 
          from their means.” 
[al-Nisaa’ 
          4:34]
If the 
          woman foregoes this right, to which she is entitled – which is her maintenance– 
          then it is no longer obligatory upon her husband.  
Ibn 
          Qudaamah said: If she agrees to forego some part of her share (of her 
          husband’s time) or her maintenance, or all of that, this is permissible. 
          (al-Mughni, vol. 7, p. 244).  
With 
          regard to the permission and approval of the first wife for a plural 
          marriage, this is not a condition and the husband does not have to seek 
          the permission of his first wife to marry a second. But it is prescribed 
          for him to be kind to her and to spend money and to say kind words so 
          as to calm her down and reduce her jealousy. The Standing Committee 
          was asked about the first wife’s approval for one who wants to marry 
          another wife. Their response was:  
It is not obligatory for the husband, 
          if he wants to take a second wife, to have the approval of the first 
          wife, but it is the matter of good manners and kind treatment that he 
          should speak to her kindly in such a way as to reduce the feelings of 
          hurt which are natural in women in such cases.  That is by smiling 
          at her, showing that he is happy to see her, being kind, speaking nicely 
          and by spending money on her if necessary.  
See 
          Fataawa Islamiyyah, vol. 3, p. 204