Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.057.

Section : Whose imamate is not acceptable.

It is not allowed for one who has a health problem which does not allow him to remain in a state of purity to be an imam for others who do not have such a problem. This is the opinion of the majority of the scholars. According to the Maliki school, such a person’s imamate will be valid, but it is disliked to make such a person the imam.