Can I cross in front of a man praying without a Sutrah from distance of about 10 or 15 feet away or should I wait till he finished this prayer? Could you explain this according to Sunnah?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is desirable for a person who is praying to take a Sutrah (some sort of partition) and to be close enough to it to prevent others from passing in front of him. But taking a Sutrah becomes obligatory if he fears that other people may pass in front of him, and he has to prevent any human being or animal from passing in front of him.

According to the preponderant opinion among scholars, it is forbidden to pass in front of the one who is performing obligatory/optional prayer, whether or not there is a Sutrah, and whether or not one can find an alternative.

The above ruling does not apply in the area of circumambulation around the Ka'bah, since there is an evidence that supports such an exception. Also, one who is forced due to an unavoidable need can pass in front of the one who is praying. Al-Bukhari reported from Abu Saalih As-Sammaan who said, “I saw Abu Sa'eed Al-Khudri praying on Friday, behind something which acted as a Sutrah. A young man from Bani Abu Mu'ait wanted to pass in front of him, but Abu Sa'eed repulsed him with a push on his chest. Finding no alternative, he again tried to pass but Abu Sa'eed pushed him with a greater force. The young man abused Abu Sa'eed and went to Marwaan and lodged a complaint against him. Abu Sa'eed followed the young man to Marwaan who asked him: 'O Abu Sa'eed! What happened between you and the son of your brother? Abu Sa'eed said to him: “I heard the Prophet saying: ‘If anybody amongst you is praying behind something as a Sutrah and somebody tries to pass in front of him, then he should repulse him, and if he refuses, he should use force against him for he is a Satan; i.e., in such an action.’”

Besides, 'Abu Juhaym narrated that the Prophet said: “If one knew (the sin) of passing in front of one who is praying, he would rather wait for forty than to pass in front of him. Abu An-Nadhr - one of the Hadeeth narrators – said: ‘I do not remember exactly whether he said forty days, months, or years.’” [Al-Bukhari and Muslim]

Ibn Hajar said: “According to such Hadeeth, it is completely forbidden to pass in front of one who is praying until he finishes his prayer even if there is no other choice. The Hadeeth of Abu Sa'eed supports such an opinion.”

As for the distance that you should leave between you and the one who is praying if there is no Sutrah, then there is no clear and sound evidence in this concern. Thus, scholars differ about this point.

Some scholars believe that the distance ends with the place sufficient for Rukoo’ (bowing down) and Sujood (prostration) of a praying person.

Other scholars believe that the Sutrah equals to three arm spans.

According to some others, like Shaykh Ibn Baaz such an issue is governed by people's custom; i.e., the Sutrah ruling is fixed according to people's judgment and consideration. This last opinion is based on the scholars’ decision that states: “If some term is not explained and specified in the Sharee'ah or in language, then it is governed by custom.”

For more benefit on Sutrah, please refer to Fataawa 53945, 84045, 89048 and 106812.

Allah knows best.