Sahih Muslim | Book 6 | Hadith Number 2382

Narrated by Abu Huraira (Allah be pleased with him)
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (may peace be upon him)as saying: Do not observe fast for a day, or two days ahead of Ramadan except a person who is in the habit of observing a particular fast; he may fast on that day.