The eighth directive is that things should be weighed and measured with honesty. The Almighty says that He has set the earth and the heavens on a scale and thus it is necessary that a person in his circle should remain just and measure with the right scale and weights. The Qur’ān says:

وَالسَّمَاء رَفَعَهَا وَوَضَعَ الْمِيزَانَ أَلَّا تَطْغَوْا فِي الْمِيزَانِ وَأَقِيمُوا الْوَزْنَ بِالْقِسْطِ وَلَا تُخْسِرُوا الْمِيزَانَ (55: 7-9)
And He raised high the heaven and set the scale of all things that you might not transgress that scale. Give just weight and full measure. (55:7-9)

It is evident from these verses that this is a very important directive and in its essence is actually a corollary of the scale of justice on which this world has been created. Thus if anyone deviates from it, it means that his conception of justice and fairness has become defective and he actually does not believe in a just God. After this, obviously the economic and social systems of the society are shaken from their bases and no ingredient of the society remains in its place. The people of the Prophet Shu‘ayb (sws) were involved in such malpractices. At more than one instance, his advice and sermon to his people in this regard is mentioned in the Qur’ān. At one place, it is said:

أَوْفُوا الْكَيْلَ وَلَا تَكُونُوا مِنَ الْمُخْسِرِينَ وَزِنُوا بِالْقِسْطَاسِ الْمُسْتَقِيمِ وَلَا تَبْخَسُوا النَّاسَ أَشْيَاءهُمْ وَلَا تَعْثَوْا فِي الْأَرْضِ مُفْسِدِينَ (26: 181-183)
Give just measure and defraud none. Weigh with the right scales and do not cheat your fellow men of what is rightly theirs; and do not spread anarchy in the land. (26:181-183)

Adulteration in things is also a similar case. If a person mixes water in milk, or sand in sugar or wheat in grain, he commits the same crime because even if he weighs accurately he is not giving the buyer in full what he is buying. This is like usurping the rights of others for which he will have to face grave consequences both in this world and in that to come. Thus the Qur’ān has said: “give full measure, when you measure, and weigh with correct scales. This is better and fairer as far as the consequences are concerned.”