Prayer: Using a Barrier or Distance During Prayer
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 874
If a man and a woman stand level with each other or a woman stands in front and they perform prayers, and if there is a wall, curtain, or something else between them so that they cannot see one another, or the distance between them is more than ten cubits (dhirāʿs) (equivalent to approximately four and a half metres), then in these cases, the prayers of both of them are valid.
The seventh condition: The place of one’s forehead must not be higher or lower than the height of four fingers closed together in relation to the place of his knees and big toes. The details of this ruling will be mentioned in the section on sajdah.