The Ruling on Praying on a Chair in the Obligatory and Voluntary Prayers

Question:
May Allah reward you for the questions asked. Honorable Shaykh, she mentions that she is an eighteen-year-old girl who prayed on a chair for a week on the doctor's orders due to pain in her knees. Sometimes she says, "When I feel tired and in pain, I pray on a chair, and sometimes I pray the obligatory prayer standing and the voluntary prayer on a chair. Is my prayer valid?"

Answer:
Yes, the valid prayer, if one is unable to prostrate and only sits on a chair, and is unable to bend his legs or knees, and sitting on the chair is more comfortable for him, then there is no blame on him for that. His saying (peace and blessings be upon him): "The sick man prays standing, and if he cannot, then sitting, and if he cannot, then on his side." Allah the Exalted said: As for the voluntary prayer, it is permissible for the standing person and the sitting person, even if he has no illness and even if he has no excuse. As for the obligatory prayer, standing is a pillar in it with the ability, and if he is unable, he prays sitting on the ground or on a chair, and he indicates his bowing and prostration. Yes.