Muhammad bin Yahya, that is al-Dhuhli (may Allah have mercy on him), says: "I borrowed the sa' of Malik bin Anas from Isma'il bin Abi Uways, and I found written on it: 'The sa' of Malik bin Anas, calibrated to the sa' of the Prophet (peace and blessings be upon him).' I believe I calibrated it with lentils, and I found it to be five and a third ratls."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7723