Allah the Exalted said «وإذا كالوهم أو وزنوهم يخسرون‏» "When they give by measure or weight to others, they give less." The meaning is that the sellers measure and weigh for the buyers. Just as in another verse, the word «يسمعونكم‏» means «يسمعون لكم‏.‏» , similarly in this verse, «كالوهم» means «كالوا لهم» . The Prophet (peace and blessings of Allah be upon him) said: "Measure the dates and take the full price for your camel." And it is narrated from Uthman (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said to him: "When you sell something, give it by measure, and when you buy something, have it measured for you."

Narrated `Abdullah ibn `Umar: Allah's Apostle said, "He who buys foodstuff should not sell it till he is satisfied with the measure with which he has bought it.