Sufyan bin Uyaynah narrated to us; he said: Sufyan al-Thawri said to me: "Do you have anything of food (provision)?" I said: No, nothing. He said: Then afterwards I mentioned a hadith; Ma'mar narrated it to us from al-Zuhri, from Malik, from Umar (may Allah be pleased with him), that "the Prophet (peace and blessings be upon him) used to sell the dates of Banu al-Nadir and would keep back for his family their provision for a year."
Al-Bukhari (may Allah have mercy on him) narrated it in the Sahih from Muhammad bin Salam, from Waki'.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النفقات / 15700