The sick person's prayer: concessions by capacity

Illness does not cancel the prayer, it lightens its form. Ibn al-Mundhir states that he knows no scholar who prevents the sick person from staying behind congregations because of his illness: the Prophet (peace and blessings of Allah be upon him) himself, when he fell ill at his end, stayed home and ordered: "order Abu Bakr to lead the people in prayer" (al-Bukhari 664, Muslim 313).

Praying standing, seated, lying down

Whoever can stand prays standing. If he cannot, he prays seated; if he cannot, he prays lying down, by signs. The Prophet visited a sick man who was prostrating on a staff; he removed it, took a cushion, then told him to leave it if he could prostrate on the ground, otherwise to make signs (reported by Malik in one transmission and with a sound chain).

The sick imam prays seated

The imam has only been established to be followed: do not differ with him; if he prays seated, pray all of you seated.al-Bukhari 656, Muslim 412

Ahmad reports that four Companions led the prayer seated after the Prophet: Usayd ibn Hudhayr, Qays ibn Fahd, Jabir ibn Abdallah and Abu Hurayra. Some scholars nevertheless prefer to appoint a standing imam when one exists, so that the followers' prayer remains complete.

The sick person's prostration

The sick person bows and prostrates with head gestures when he cannot place the members. Raising onto an elevated object at face height is not accepted by the jurists as a substitute for prostration: indication by sign is the way, as the staff episode shows.

Practical note

The sick person does not let the times pass: he prays each prayer within its time, in the posture his body allows. Changing posture does not reduce validity, only the scope of the rite, and Allah asks for effort proportionate to ability.