Reference: http://www.alfawzan.af.org.sa/node/16123
Question: [Performing] the prayer [whilst seated] on chairs has become widespread in the mosques; [so] is [the performance of] the prayer [whilst sitting] on a chair better, or [whilst sitting] on the floor – because of the prostration and the rest of the [required] pillars of the prayer?
Response: The base principle [in this matter] is [the requirement] to sit on the floor; however, whoever is unable to sit on the floor, can sit on a chair. And if he is able to prostrate on the floor – what I mean is that he sits on the chair during the standing part [of the prayer], then he prostrates on the floor [when required to do so] – this is mandatory for him to do. And if he is unable to prostrate on the floor, then [whilst seated on the chair] he must motion himself [forward a little] to do the prostration; so he motions himself to do the prostration by [dropping] his neck and head forward [a little] – and this will suffice [him] instead of the prostration on the floor. This is based on His (Subhaanahu wa Ta’aala) saying:
{So fear Allaah as much as you are able} – soorah at-Taghaabun, aayah 16.
