Ibn al-Musayyib (may Allah have mercy on him) says: I saw Sayyiduna Abu Hurayrah (may Allah be pleased with him) walking around the market; then he came to his family and said: Do you have anything? If they said: No, he would say: Then I am fasting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7918