It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) in a marfu’ form that when any one of you intends to pray, he should place something in front of him (as a sutrah). If he does not find anything, then he should stand a staff upright, and if there is not even a staff, then he should draw a line. After that, whatever passes in front of him, it does not matter.