Examples of harming the neighbors:
Examples of harming the neighbors are numerous. The most common of them are: Looking to their inviolable matters, looking at their wives and their secret things, following their faults, spying on their personal affairs, revealing their secrets, backbiting them, violating their honor, seeking the stirring up of discord between them, propagating their faults, concealing their good traits, turning up the sound of the musical instruments of prohibited singing, producing annoying sounds, particularly during the times of their sleep and rest.
Additionally, harming them by placing animals and birds which give off offensive odors and annoying sounds as well as placing the rubbish and the like in front of their doors.
The very vicious of neighbors is the one whose neighbors abandon him in order to avoid his evil, harm, aggression and scheme.
The more vicious is the one who violates his neighbor's honor or steals from his money. The Prophet, sallallaahu ‘alayhi wa sallam, was asked: "Which sin is the gravest in the sight of Allah?" He, sallallaahu ‘alayhi wa sallam, replied: "That you associate a partner with Allah (despite the fact) that He has created you. He, sallallaahu ‘alayhi wa sallam, was also asked: "What is the next (gravest sin)?" He, sallallaahu ‘alayhi wa sallam, replied: "That you kill your child out of fear that he shall join you in food." Then,, he, sallallaahu ‘alayhi wa sallam, was asked: "What is the next (gravest sin)?" He, sallallaahu ‘alayhi wa sallam, replied: "That you commit adultery with the wife of your neighbor." 
Al-Miqdaad Ibn Al-Aswad narrated that the Messenger of Allah asked his Companions: "What do you say about adultery." They said: "It is prohibited, as Allah and His Messenger have prohibited it. So it is forbidden until the Day of Judgment." The Messenger of Allah said: "For a man to commit adultery with his neighbor's wife is worse than if he commits adultery with ten women." He, sallallaahu ‘alayhi wa sallam, then said: "What do you say about theft." They said: "It is prohibited, as Allah and His Messenger have prohibited it." He, sallallaahu ‘alayhi wa sallam, said: "If a man steals from his neighbor, it is worse for him than stealing from ten homes." 
Since the right of the neighbor towards his brother was great, and his knowledge of his affairs and his ability to betray and deceive him due to his neighborhood and adjacency were exceeding other than him, so violating his honor by committing adultery with his wife and unmarriageable women or stealing his money is greater in sin and offense.