What is the ruling in Islam if you have been overpaid by your employers, undercharged when purchasing an item, given too much change and if your phone company has accidentally credited your account with some money.


Praise be to Allaah.
 

Firstly: in all the cases mentioned above, you must give back
to people what is their due. It is not permissible for you to take the money
of other people if they forget or make a mistake. What you have been given
does not belong to you and it is not permissible for you to take it. If
something is credited to your account by mistake or because of
forgetfulness, it is not permissible for you to take it. This is indicated
by all the evidence of sharee’ah. 

Allaah says (interpretation of the meaning): 

“O you who believe! Eat not up your property among
yourselves unjustly except it be a trade amongst you, by mutual consent”

[al-Nisa’ 4:29] 

“Verily, Allaah commands that you should render back the
trusts to those, to whom they are due; and that when you judge between men,
you judge with justice. Verily, how excellent is the teaching which He
(Allaah) gives you! Truly, Allaah is Ever All-Hearer, All-Seer”

[al-Nisa’ 4:58] 

It was narrated from Abu Hurayrah that the Prophet
(peace and blessings of Allaah be upon him) said: “The signs of a hypocrite
are three: when he speaks he lies, when he makes a promise he breaks it, and
when he is entrusted with something he breaks that trust.” (Narrated by
al-Bukhaari, 33; Muslim, 59). 

Ahmad (94, 23) narrated that the Prophet (peace and
blessings of Allaah be upon him) said: “It is not permissible for a man to
take his brother’s wealth unlawfully.” That is because Allaah has forbidden
the Muslim to take his fellow-Muslim’s wealth. 

According to a report narrated by Ibn Hibbaan (13/317): The
Messenger of Allaah (peace and blessings of Allaah be upon him) said:
“It is not permissible for a Muslim to take his brother’s stick without his
consent.” Classed as saheeh by Shaykh al-Albaani in Ghaayat al-Muraam,
456. 

It was narrated that Abu Humayd al-Saa’idi said: The
Messenger of Allaah (peace and blessings of Allaah be upon him) said:
“… By Allaah, no one of you takes something unlawfully but he will meet
Allaah carrying it on the Day of Resurrection. So I will recognize one of
you meeting Allaah carrying a camel bellowing, or a cow mooing, or a sheep
bleating.” Then he raised his hand until the whiteness of his armpit could
be seen, and he said, “O Allaah, have I conveyed (the message)?” 

Narrated by al-Bukhaari, 6578; Muslim, 1832. 

Secondly: 

But if the owner of the money has given you more than you are
entitled to, then that belongs to you and there is nothing wrong with that,
because the Prophet (peace and blessings of Allaah be upon him) said:
“Whatever of this wealth comes to you and you were not hoping for it or
asking for it, then take it, otherwise do not hope for it.” (Narrated by
al-Bukhaari, 1473; Muslim, 1045).

 And Allaah knows best.