(14) باب لاَ يَتَقَدَّمَنَّ رَمَضَانَ بِصَوْمِ يَوْمٍ وَلاَ يَوْمَيْنِ
Narrated Abu Huraira:
The Prophet (ﷺ) said, "None of you should fast a day or two before the month of Ramadan unless he has the habit of fasting (Nawafil) (and if his fasting coincides with that day) then he can fast that day."
Reference: Sahih al-Bukhari 1914
In-book reference: Book 30, Hadith 24
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 31, Hadith 138