he should pray according to his ability—whether seated or lying on his side—for the Prophet (peace and blessings be upon him) said: “Pray standing; if you cannot, then pray sitting, and if you are unable, then pray on your side.” Thus, what your father does—praying while seated because of pain in his knee—poses no problem so long as that pain prevents him from standing or makes it unduly difficult. If, however, the pain does not stop him from standing, his prayer is not valid unless he stands, for standing is one of its pillars.
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Opening supplication of the prayer
Question: I am a man who prays and fasts, all praise is due to Allah. When I turn toward the qiblah I say, “I have turned my face to Him who created the heavens and the earth, as a pure monotheist. Indeed, my prayer, my sacrifice, my living and my dying are for Allah, Lord of the worlds.” Is saying this part of the Sunnah or not?
Answer: This supplication is not to be recited merely when you face the qiblah; rather, it is recommended to say it after the takbīrat al-iḥrām (the opening takbīr), because it is one of the opening invocations reported from the Prophet (peace and blessings be upon him). Sometimes, after pronouncing the takbīrat al-iḥrām, he would begin the prayer by saying: “I have turned my face toward Him who created the heavens and the earth, inclining solely to Him, and I am not of the polytheists. Indeed, my prayer, my sacrifice, my living and my dying are for Allah, Lord of the worlds; He has no partner, and I am the first of the Muslims.” This is therefore one of the several opening invocations with which the Messenger of Allah (peace and blessings be upon him) would start his prayer after the takbīrat al-iḥrām. Its proper place is after the opening takbīr, not when turning toward the qiblah and before the takbīrat al-iḥrām.