Mukhtasar Bukhari

Narrated by Sayyiduna Abu Huraira (may Allah be pleased with him) from the Noble Prophet (peace and blessings of Allah be upon him) that he (peace be upon him) said: "None of you should fast a day or two before Ramadan. However, if a person has a habit of fasting on a particular day and that day coincides (with these days), then he may fast on that day. (Specifically, it is not permissible to fast with the intention of welcoming Ramadan.)"