“The Messenger of Allah (ﷺ)
used
to say from the pulpit, before the month of Ramadan: ‘Fasting
will
begin on such and such a day, but we are going to start fasting
earlier, so whoever wants to start fasting earlier (i.e., in
Sha’ban),
let him do so, and whoever wants to wait until Ramadan
begins, let him
do so.’”
Sunan Ibn Majah Book 7, Hadith 10