Anas bin Sirin reported,

We came to Anas bin Malik on a Thursday. He called for his table and invited the people to lunch. Some of them ate while others abstained. Then they came to him again on Monday, and he did the same. He called for his table and invited them to lunch. Some of them ate while others abstained.Anas bin Malik said to them, "Perhaps you are Monday-fasters? Perhaps you are Thursday-fasters? The Messenger of Allah ﷺ used to fast continuously without breaking his fast, until we would say that he did not intend to break his fast that year. Then he would stop fasting and not fast at all, until we would say that he did not intend to fast that year. The fasting he loved most was in Shaban."

حدثنا يونس حدثنا عثمان بن رشيد قال

حدثني أنس بن سيرين قال

أتينا أنس بن مالك في يوم خميس فدعا بمائدته فدعاهم إلى الغداء فتغدى بعض القوم وأمسك بعض ثم أتوه يوم الاثنين ففعل مثلها فدعا بمائدته ثم دعاهم إلى الغداء فأكل بعض القوم وأمسك بعض فقال لهم أنس بن مالك لعلكم اثنانيون لعلكم خميسيون كان رسول الله ﷺ يصوم فلا يفطر حتى نقول ما في نفس رسول الله ﷺ أن يفطر العام ثم يفطر فلا يصوم حتى نقول ما في نفسه أن يصوم العام وكان أحب الصوم إليه في شعبان