Question: Through this letter, I would like to inform you that my mother has now reached miserable old age, where she is unaware of anything regarding religion or worldly affairs. She can only recognize my voice. She cannot differentiate night from day, nor can she recognize anything else. The matter of the obligation of Sawm (fast) on her bewilders me. Is there any Kaffaarah (expiation) obligatory on her, since she is so disabled that she cannot carry out any of the pillars of Islaam? It should be known that this is not due to negligence, laziness, or Kufr (disbelief) on her part. Rather, this is due to old age.
Please give me your Fatwaa (legal opinion issued by qualified Muslim scholar). Is it obligatory on us to feed the poor on her behalf? May Allaah guide you and grant you success.
Answer: If the reality is as you mentioned, your mother owes nothing, since she is no longer Mukallaf (person meeting the conditions to be held legally accountable for their actions), because she lost her memory as a result of her old age… read more here.