Answer
(Fatwa: 130/L=49/TL=1434)
In the question mentioned above, first the person who is offering salah on chair should think whether he needs to offer salah on chair as per the Shariah or not. A detailed fatwa is available on our Darul Ifta website. If someone is really entitled to offer salah on chair then it is lawful for those who offer salah on chair to offer it in various parts of the masjid. However it is better for them to offer salah on the end of saf (row) so that the gap which is caused by putting the chair could not take place as hadith speaks extensively about making the saf straight and standing shoulder to shoulder. You should make them understand politely and tell them the hadith, you do not have the right to ask them to go to the end or put their chairs on the end of the saf.
وليس له از عاج غيره منه ولو مدرسا وeبفي الشامية قوله ليس له الخ قال في القنية: له في المسجد موضع معين يواظب عليه وقد شغله غيره قال الاوزاعى له أن يزعجه وليس له ذلك عندنا، اي المسجد ليس ملكا لأحد (شامي).
The correct method of putting the chair in the saf is that the chairs are put in the saf in a way that its hind legs are in the level of the muqtadi’s heels so that the shoulders of the people offering salah on chair are in the level of muqtadis offering salah on chair as hadith speaks about keeping the shoulders even and straight along with the straightening of saf.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband