When one of you stands up to pray, he should put a screen in front of him as tall as the height of the back of a saddle. If he does not have something the height of the back of a saddle in front of him, his prayer would be invalidated if a donkey, a woman, or a black dog passed in front of him

When someone stands up to pray, he should place a screen the height of the back of a saddle (approximately two-thirds of a cubit) in front of him, otherwise his prayer would be invalidated by the passing of any one of these three in front of him: a woman - restricted to a menstruating woman in the narration of Abu Dawūd - a donkey, or a black dog.

However, if he places a screen in front of him, his prayer will be valid regardless of anything passing by on the other side of the screen, including those three. The narrator, ‘Abdullāh ibn As-Sāmit, asked: “O Abu Dharr: "What is the difference between a black dog and a red or a yellow dog?” Meaning: why did the Prophet (may Allah's peace and blessings be upon him) single out a black dog?

He said: “O nephew, I asked the Messenger of Allah (may Allah's peace and blessings be upon him) the same question, and he answered: "A black dog is a devil.” According to the Saudi Arabian Permanent Committee for Scholarly Research and Iftā', this Hadīth means that the passing of a woman, a donkey, or a black dog in front of someone praying, renders the prayer void.

However, some scholars thought that the intended meaning was that one’s focus in prayer would be interrupted or the prayer’s perfection would be compromised, rather than it would render the prayer void or invalid.