Answer
(Fatwa: 947/893=D/1429)
It is better not to stand in back row alone in salah. One should take any musalli from the front row and make him stand with him. But this ruling is applicable only when people are aware of it; so that on one who is taken back does not spoil his salah or start quarrelling due to ignorance of the ruling. Commonly, people are not aware of such kinds of rulings. Also, many new musallis keep on joining the congregation, due to this very reason it is better not to take a musalli from the front row.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband