Abu Uthman narrates: Sayyiduna Abu Hurairah (may Allah be pleased with him) was traveling when the people camped and spread out the dining cloth. The people sent someone to call Sayyiduna Abu Hurairah (may Allah be pleased with him), and at that time he was performing prayer. He informed them: I am fasting. When the people finished eating, Sayyiduna Abu Hurairah (may Allah be pleased with him) came. He began to eat. The people sent their messenger towards him. He said: Why are you looking at me? By Allah! He had told me that he was fasting. So Sayyiduna Abu Hurairah (may Allah be pleased with him) said: He spoke the truth. I heard the Prophet (peace and blessings be upon him) say: "Whoever fasts three days in every month, it is as if he has fasted the whole month." So I fast three days every month, thus it is as if I fast the whole month, and I have found confirmation of this in the Book of Allah, the Exalted (the statement of Allah, the Exalted): "Whoever brings a good deed, he will have ten times the like thereof."
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3659
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الإرواء» (4/ 99 / 946).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم