Sunan Abu Dawud
2335
Sahih+3

Narrated Abu Hurairah:The Messenger of Allah (ﷺ) as saying: Do not fast one day or two days just before Ramadan, except in the case of a man who has been in the habit of observing the particular fast, for he may fast on that day

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid