Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "The mikyal (measuring vessel) of the people of Madinah is the one to be relied upon, and the standards of weight shall be those of the people of Makkah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11159
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "The measure of the people of Makkah and the weight of the people of Madinah are the ones to be relied upon."
Sulayman (al-Tabarani) said: Abu Ahmad narrated it in this way, saying "from Ibn Abbas", and so he differed from Abu Nu'aym in the wording of the hadith; what is correct is what Abu Nu'aym narrated, in both chain and wording.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11160