then draw a line. But how should he draw it? Should he draw a curved line like a crescent, or one extending straight like a staff? (1)

The answer is: any line will suffice. Hence the author says, “facing a line,” without specifying its form. Likewise, the hadith says, “let him draw a line.” This line serves as a marker for the one praying and is beneficial to him.

The prayer is invalidated only by the passing of a solid-black dog. ..............

His statement, “is invalidated,” refers to the prayer, including both obligatory and voluntary prayers. Invalidity is sometimes used for that which was never validly commenced, and sometimes for that which was validly commenced and then became invalid. The latter is more common; that is, the scholars use invalidity for that which was validly commenced and then became invalid, though they may also use it for that which was never validly commenced. For example, if it is said, “If he omits the opening takbir, his prayer is invalid,” this refers to something that was never validly commenced. Likewise, if it is said, “A sale is invalid if the price is unknown,” this refers to something that was never validly commenced. The author’s statement here, “is invalidated by the passing of …,” refers to something that was validly commenced and then became invalid.

His statement, “by the passing of a dog,” means the dog crossing from the worshipper’s right to his left, or from his left to his right. As for a dog climbing up in front of the worshipper, this does not invalidate the prayer. Thus, if we suppose that there is a dog in front of you, your prayer is not invalidated.

His statement, “by the passing of a dog”: a dog is a well-known animal.

His statement, “black,” means not red, white, blue, or any colour other than black.