"The Messenger of Allah said: "Volume is to be measured according to the system of the people of Al-Madinah, and weight is to be measured according to the system of the peole of Makkah."' (Sahih) This is the wording of Ishaq (one of the narrators).
Sunan an-Nasa'i Book 44, Hadith 146
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Sunan an-Nasa'i Book 44, Hadith 147