Sunan an Nasai
2177
Hasan Sahih+2

It was narrated from Abu Salamah bin 'Abdur-Rahman that he asked Aishah about the fasting of the Messenger of Allah. She said:"The Messenger of Allah used to fast until we said: 'He will not fast.' And he used to fast Shaban, or most of Shaban

Hasan SahihAbu Ghuddah
Hasan SahihAl-Albani