If it is said: Suppose he covers it with soil—will his prayer be valid?

The answer is: if the soil is thick enough that he would not come into contact with the impurity when he presses down upon it, then the prayer is valid. But if it is thin enough that he would touch the impurity when he presses down upon it, then the prayer is invalid.

“If it is at the edge of a connected prayer mat, the prayer is valid, provided it does not move along with him when he walks …”

His statement, “If it is,” refers to the impurity.

His statement, “at the edge of a connected prayer mat, the prayer is valid,” may be illustrated by a man praying on a rug whose edge is impure. This edge is connected to the part upon which he is praying, but he neither directly touches nor comes into contact with the impurity. We therefore say that his prayer is valid.

His statement, “provided it does not move along with him when he walks,” is somewhat awkwardly worded. It does not fit with the preceding statement except by an implied qualification, because when he says, “if it is at the edge of a prayer mat,” a prayer mat does not move along when one walks; if you walk, it remains in its place. However, the author is alluding to another issue: when the impurity is connected to something attached to the worshipper. If it moves along with him when he walks, his prayer is invalid; but if it does not move along with him, his prayer is valid.

An example is a man holding a rope which he has tied around a donkey’s neck, either in his hand or around his waist. In this case, his prayer is valid, because if the donkey were to resist him, it would not be pulled along when he walks—this is generally the case. Thus, the prayer is valid, because the man is not carrying the impurity, the impurity is not following him, and he is not directly touching it. This is according to the view that a donkey is impure.

A second example is another man who ties a rope to his hand or around his waist, and ties its other end around the neck of a small dog. This man’s prayer is invalid, because when he walks, the dog is pulled along with him; he is therefore now causing the impurity to follow him.