Allah, exalted be His praise, says: "Then its expiation is feeding ten poor persons from the average of what you feed your families" [Surah al-Ma'idah: 89].
Imam al-Shafi'i (may Allah have mercy on him) said: "In the expiation for an oath, one mudd (per poor person) by the mudd of the Prophet (peace and blessings be upon him) suffices, because a 'araq (basket) of dates was brought to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) gave it to a man and ordered him to feed sixty poor persons with it. The 'araq is estimated at fifteen sa', which makes sixty mudd, one mudd for each poor person."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / Q19968