Mukhtasar Bukhari (Abridged) 587 — If unable to sit, pray lying

Sayyiduna Imran bin Husain (may Allah be pleased with him) says: I had hemorrhoids, so I asked the Messenger of Allah (peace and blessings of Allah be upon him) about prayer—whether it is permissible to pray while sitting. He (peace and blessings of Allah be upon him) said: "Pray standing, and if you are not able, then sitting, and if you are not able to sit, then lie on your side and pray."