Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "In measuring by volume, the measure of the people of Makkah is to be relied upon, and in weighing, the weight of the people of Madinah is to be relied upon."
Al-Bazzar recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب البيوع / 6337