Imam Ja'far al-Sadiq, may Allah have mercy on him, narrates from his father (Imam Baqir, may Allah be pleased with him), who narrates from Imam Zain al-Abidin, may Allah have mercy on him, who narrates from Imam Husayn, may Allah be pleased with him, who narrates from Sayyiduna Ali, may Allah be pleased with him, who narrates from the Prophet Muhammad, peace and blessings be upon him: "If a sick person is able to perform the prayer standing, then he should perform it standing; otherwise, he should perform it sitting. If he is not able to perform prostration, then he should indicate the prostration with a gesture, and his prostration should be lower than his bowing. If he is not able to perform the prayer sitting, then he should perform the prayer lying on his right side facing the qiblah. If he is not able to perform the prayer even on his right side, then he should perform the prayer lying flat, and both his feet should be facing the qiblah."