Muwatta' Malik 686

Yahya related to me from Malik that he had heard the people of knowledge telling people not to fast on the day in Shaban when there was doubt (about whether it was Shaban or Ramadan), if they intended by it the fast of Ramadan . They considered that whoever fasted on that day without having seen (the new moon) had to make up that day if it later became clear that it was part of Ramadan. They did not see any harm in voluntary fasting on that day. Malik said, "This is what we do, and what I have seen the people of knowledge in our city doing." Yahya related to me from Malik from Abu'n Nadr, the mawla of Umar ibn Ubaydullah, from Abu Salama ibn Abd ar-Rahman that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "The Messenger of Allah, may Allah bless him and grant him peace, used to fast for so long that we thought he would never stop fasting, and he would go without fasting for so long that we thought he would never fast again. I never saw the Messenger of Allah, may Allah bless him and grant him peace, fast for a complete month except for Ramadan, and I never saw him do more fasting in any one month than he did in Shaban