Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Hakam that during the time of the Holy Prophet (peace and blessings be upon him), wheat and other goods arrived for Hazrat Uthman (may Allah be pleased with him). The Prophet (peace and blessings be upon him) said: "Come with us to Hazrat Uthman (may Allah be pleased with him) so that we may help him in selling the wheat." The Prophet (peace and blessings be upon him) stood by his side. Hazrat Uthman (may Allah be pleased with him) was saying that there is such and such amount of wheat in this sack and I will sell it for such and such price. The Prophet (peace and blessings be upon him) said: "When you specify by name, then measure it out."

Hazrat Ibn Sirin says that when the measure and weight are specified by name, do not sell it forward before it has been measured.

Hazrat Qatadah and Hasan (may Allah have mercy on them) say that when the measure and weight are specified by name, then the measuring should be done.

Ibrahim (may Allah have mercy on him) said: When you choose Salam (advance payment sale) and specify the measure, then do not take it by estimation.

Hazrat Sha'bi (may Allah have mercy on him) says that when you have to sell something by measure, then measure it properly.