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