If a person is performing Salaat in a big Musjid then it will be permissible
for one to walk across at least 2 or 3 Saffs in front of him. If it is a
small Masjid / Musalla, then it will not be permissible to walk in front of
him at all. If the size of the Musjid is 235 square meters, then it will be
considered to be big and if less then small. (Ahsanul Fataawa vol.3 pg.409;
HM Saeed)
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai