Abu Hurairah (May Allah be pleased with him) reported:
The Prophet (ﷺ) said, "Do not observe Saum (fasting) for a day or two days preceding Ramadan. However, if a person is in the habit of observing Saum on a particular day (which may fall on these dates), he may fast on that day."[Al-Bukhari and Muslim].
App reference: Book 9, Hadith 234
Arabic/English book reference: Book 9, Hadith 1224