What is the ruling for an Imam who is sick and unable to stand during prayer?
Chapter on Imamate and Congregational Prayer
Al-Mughni
Book of Prayer
Primary text
If the Imam falls ill and is unable to stand, it is recommended that he appoint a deputy (Istikhlaf). This is to avoid differing opinions regarding the validity of his leadership while seated, and because the prayer of a standing person is more complete. The Prophet (peace be upon him) prayed seated to demonstrate its permissibility and appointed a deputy on another occasion. The prayer of the Prophet seated is superior to the prayer of others standing.
Supporting text
If the Imam prays seated, the followers should pray seated behind him. Four Companions performed this: Usayd ibn Hudayr, Jabir, Qays ibn Qahd, and Abu Hurayrah. This was also the view of Al-Awza'i, Hammad ibn Zayd, Ishaq, and Ibn al-Mundhir. Malik, in one narration, held that the prayer of one capable of standing behind a seated Imam is invalid, a view shared by Muhammad ibn al-Hasan. Their evidence is the narration from Al-Sha'bi, from the Prophet (peace be upon him), stating, "No one shall lead others in prayer after me while seated," narrated by Al-Daraqutni, and because standing is a pillar (rukn), the one capable of it cannot follow someone unable to fulfill it, similar to other pillars.