Is it permissible for a man to lead people in a congregational obligatory prayer while he is sitting on a chair and gesturing for prostration?

It is permissible for a person who cannot stand to lead in prayer others who are also unable to stand, according to the consensus of the majority of jurists. As for those who are able to stand, his imamate for them is not valid according to the Malikis, while the Hanafis and Shafi'is permit it. The Hanbalis hold that the imamate is valid if the imam is a regular imam and his inability is temporary. This last opinion is the most preferred.