Is it permissible to pass in front of worshippers to perform the supererogatory prayer of 'Isha (Sunnah Ratibah), or the Shaf' and Witr prayers, after completing the 'Isha obligatory prayer?

It is permissible to pass behind the sutra of a praying person. However, if one prays without a sutra, it is permissible to pass at a distance from him. The criterion for distance and proximity is custom or the place of prostration. It has also been said to be three cubits from the feet of the praying person. It is not permissible to pass between the praying person and his sutra, or to pass close to him if he is not praying towards a sutra.