God says
… He who deceives shall be faced with his deceit on the Day of Resurrection, when every person will be paid in full for what he has done… Q.3:161
… And [in all your dealings] give full measures and weight in equity: [however,] We do not burden any human being with more than he is well able to bear; …* Q.6:152
* The meaning is that God does not expect man to behave with “mathematical” equity – which, in view of the many intangible factors involved, is rarely attainable in human dealings – but expects him to do his best towards achieving this ideal.
Woe unto those who give short measures: those who, when they are to receive their due from (other) people, demand that it be given in full -- but when they have to measure or weigh whatever they owe to others, give less than what is due!* Do they not know they are bound to be raised from the dead [and called to account] on an awesome Day – the Day when all men shall stand before the Sustainer of all the worlds? -- Q.83:1-6
* The passage (1 to 3) does not, of course, refer only to commercial dealings but touches upon every aspect of social relations, both practical and moral, applying to every individual’s rights and obligations no less than to his physical possessions.
Prophet said
To those who dealt with measurements and weights the Messenger of God said: “Indeed, you have been entrusted with two affairs about which the nations in the past were destroyed ( for their fraudulence)” – H: Tirmizi. Narrator: Ibn Abbas.
(At the time) when the Holy Prophet came to Medina people there used to lend money for one to three years and the loan was paid off in the form of fruits. About this the Holy Prophet said: “He who lends money for such commodity should lend money for known measure, known weights, and to the known limit.” – H: Bukhari and Muslim. N: Abu Saeed.
