Sunan an Nasai
2351
Sahih+2

It was narrated that 'Aishah said:"The Messenger of Allah used to fast until we said: 'He will not break his fast.' And he used not to fast until we said: 'He will not fast.' And I never saw the Messenger of Allah fast more in any month than in Shaban

SahihAbu Ghuddah
SahihAl-Albani