Does hearing the sound of my married brother engaging in sexual intercourse from his adjacent room, despite his attempts to conceal the sound, constitute espionage, and should I inform him of this, and do I bear a sin for hearing this sound?

The jurists have stipulated that among the etiquettes of intercourse is that it should be away from the eyes and ears of people, and it is disliked to hear its sound. The questioner should strive to find means that prevent him from hearing his brother's and his wife's intercourse, such as closing the opening from which the sound comes, or playing the Qur'an or the radio. There is no blame upon him if something reaches him unintentionally after he has exerted efforts to prevent it.