Does the prayer become invalid if someone passes behind a prayer screen (sutrah) that was unjustly taken (ghasab)?
Chapter on Imamate and Congregational Prayer
Al-Mughni
Book of Prayer
Primary text
There are two established legal opinions regarding the validity of prayer when a dog passes behind an unjustly taken sutrah. The first opinion asserts that the prayer is invalidated. This is because the worshipper is prohibited from setting up the sutrah, rendering its presence equivalent to its absence. The second opinion maintains that the prayer is not invalidated. This position relies upon the Prophet's saying: 'That is guarded against by something like the rear part of a saddle' (referencing the sufficiency of the sutrah). Since a sutrah was present, the requirement is met.
Supporting text
The differing opinions on the sutrah issue are rooted in the fundamental legal disagreement concerning whether a prayer performed while wearing usurped clothing (ghasb) is valid; there are two transmissions of opinion on that foundational matter.