Surah No. 17, Al Isra (Bani Israel), Ayats No. 35

وَأَوْفُوا الْكَيْلَ إِذا كِلْتُمْ وَزِنُواْ بِالقِسْطَاسِ الْمُسْتَقِيمِ ذَلِكَ خَيْرٌ وَأَحْسَنُ تَأْوِيلاً

Give full measure when you measure, and weigh with a balance that is straight: that is the good and the most advantageous in the final result.

Surah No. 55, Ar Rahman, Ayats No. 8 & 9

o وَأَقِيمُوا الْوَزْنَ بِالْقِسْطِ وَلَا تُخْسِرُوا الْمِيزَانَ o أَلَّا تَطْغَوْا فِي الْمِيزَانِ

Translation :

In order that you may not do mischief with the balance, So establish the balance strictly and weigh with justice and do not fall short in the balance .