`Aaishah said: "I never saw the Messenger of Allaah fast a complete month except for Ramadan, and I have never seen him fast more in a month than he did in Sha`baan." [Bukhaari, Muslim]

Usamah ibn Zaid inquired: "O Messenger of Allaah, I never find you fasting in any month like you do during the month of Sha`baan." The Prophet responded: "That is the month the people neglect. It comes between Rajab and Ramadaan. It is a month in which the deeds are raised to the Lord of the Worlds. I love that my deeds be raised while I am fasting." [An-Nasaa'i, authenticated by ibn Khuzaimah. Hasan according to al-Albaani]

Narrated Abu Hurairah, Allaah's Messenger said: "When the month of Sha`baan is halfway, do not fast." [Reported by the five, Ahmad disapporoved it]. As-San`aanee says in Subul us-Salaam:

"One can fast provided he has to observe a compensatory fasting (in lieu of the Fard - obligatory ones) or the other prescribed ones which may be categorised as Waajib (compulsory). However, the volitional fasting is prohibited lest one should be subjected to exhaustion and weakness that may in turn render the Ramadan obligatory fasting difficult for him."

Abu Umaamah reported: "I came to the Messenger of Allaah, sallallaahu `alayhi wa sallam, and said: "Order me to do a deed that will allow me to enter Paradise." He then said: 'Stick to faasting, as there is no equivalent to it.' Then I came to him again and he said: 'Stick to fasting.'" [Ahmad, an-Nasaa'ee, al-Haakim, who said it was saheeh]

Abu Sa'eed al-Khudree reported that the Messenger of Allaah, sallallaahu `alayhi wa sallam, said: "No servant fasts on a day in the path of Allaah except that Allaah removes the hellfire seventy years further away from his face." [Related by the group, except for Abu Dawood] From Islaam.com