Volume 3, Book 34, Number 338 :
Narrated by Al-Miqdam bin Ma’diyakrib (radiallaahu `anhu)
The Prophet (sallallaahu `alayhi wasallam) said, “Measure your foodstuff and you will be blessed.”
It’s a very simple rule. No matter how much you’re tempted to make some extra money by fooling someone or giving the wrong measure, don’t do it. If you do, blessing (barakah) will be taken away from you. So even if you made a million dollars by being dishonest, you won’t find blessing in that wealth.
Honesty is the best policy. (y)