He sponsored her
    when she was an orphan and he does not want her to wear hijaab in front of him
Question

                I am a female. and, me and my brother are
      both adopted. We were brought into the house when we were only a few days old. We lived
      our lives with our adoptive parents, not knowing our conditon. After practicing Islam, I
      came to know that i was adopted. My age is now XXX. I lived with my parents until 18, then
      i married. My husband told me that i must start to wear hijaab in front of my father, and
      that he is not considered a mahram. We aksed, and someone said that we are Rabaa'b that
      Allah mentioned in the Qur'an and that hijaab need not be done. We did not feel
      comfortable and after asking further, we came to believe that He is not my Mahram, and
      that I must do hijab. My adoptive father and mother are both very emotional people.
      Whenever i mentioned adoption before, they imediately started to cry and could not talk.
      This happens all the time. Me and my husband were both scared that they would take this very badly,
      so we decided that we would be subtle in the way we took this issue. When i visited my
      adoptive parents last, i covered my hair with a type of pakistani scarf which is not
      transparent, giving the excuse that many people work around the house. Also, i did not
      wear a jilbaab, but wore lose clothes, Qamees and Sharwaal. Also i ate at the table, and
      also freely talked to my adoptive father. In front of all other non mahrams, i fully cover myself in black, even
      cover my eyes, and do not talk to men without necessity.Allah knows that the reason i am not doing full hijab is because of my
      adoptive parents would react. They are old Father XXX, mother XXX, and they are weak in
      their imaan in that they would not be able to understand nor accept this ruling in Islam.
      My father tries to pray, but misses it much, and my mother prays regularly, though missing
      some and making them up.What am I supposed
Praise be to Allah.We have to accept the rulings of sharee'ah and put them into 
  practice even if it goes against our emotions and feelings. Since there is no 
  relationship of mahram, either by blood or by radaa'ah (breastfeeding)(see Question 
  #5538) between you and the person who 
  sponsored you and brought you up, you have to observe hijaab in front of this 
  person. (For the conditions of hijaab according to sharee'ah, see Question #6991). 
  The evidence that this generous person who sponsored you has mentioned is not 
  correct and is contrary to sharee'ah. The good deeds that he has done will be 
  rewarded by Allaah if he was sincere.