Dr. Muzammil Siddiqi, former president of the Islamic Society of North America, issues the following Fatwa: “The Prophet (peace and blessings be upon him) taught us to respect the person who is praying. It is forbidden to cross in front of a praying person. It means that if you see a person praying, you should not pass between him and the place of his prostration or sujud. Give that person his place of prayer and let him pray without disturbance. This is his right and all Muslims who see him should recognize this right.
In some hadiths, it is reported that if a person would know how grave (a sin) it is to cross in front of a praying person, he would prefer to stay standing rather than passing in front of that person. The Companion who heard the hadith from the Prophet said that he did not know whether the Prophet (peace and blessings be upon him) meant forty days, forty months or forty years. (Reported by Al-Bukhari)
In addition, it is also the duty of the person praying not to stand for prayer in people’s walking areas. He may go behind a pillar or go to a corner of the Masjid. In a big and open place or in a crowded place, it is good to put some shield or sutrah between oneself and one’s place of sujud, so that other people may pass by without inconvenience. The shield could be a stick, a chair or a stool or anything about one foot high that should indicate to passers-by not to cross between that area.”