Is it permissible to pray while sitting on a chair?

The issue of praying on a chair, i.e. its ruling, depends on the opinion of a trustworthy doctor regarding the condition of the patient.

If the doctor prohibits the person from praying while seated— meaning he is unable to bend his knees on the ground, then he has no option but to pray on a chair when prostrating (sujūd).

In this case, his prayer is valid according to all the madhhabs.

If, however, the doctor prohibits the person from standing, but does not prevent him from performing other movements—such as placing his forehead on the ground during sujūd—then it is obligatory for him to do so.

And in this case, his prayer on a chair would not be valid unless he prostrates (sujūd) on the ground like everyone else.

The specific use of a chair in this scenario would have no significance or necessity.

Shaykh Dr. Muḥammad Saʿīd Ramaḍān al-Būṭī
(Translated from ‘Naseem al-Sham’ by Shaykh Mahdi Lock)