Abu Hurairah (RAA) narrated that The Messenger of Allah (ﷺ) said:
"None of you should fast a day or two before the (beginning of the) mouth of Ramadan, unless it is a day on which one is in the habit of fasting (i.e. voluntary fasting that coincides with that day)." Agreed upon.
English reference: Book 5, Hadith 671
Arabic reference: Book 5, Hadith 650