Bismillah.
Volume 3, Book 31, Number 190:
Narrated 'Aisha (radiallaahu `anhaa):
Allah's Apostle (sallallaahu `alayhi wasallam) used to fast till one would say that he would never stop fasting, and he would abandon fasting till one would say that he would never fast. I never saw Allah's Apostle (sallallaahu `alayhi wasallam) fasting for a whole month except the month of Ramadan, and did not see him fasting in any month more than in the month of Sha'ban.
Volume 3, Book 31, Number 191:
Narrated 'Aisha (radiallaahu `anhaa):
The Prophet (sallallaahu `alayhi wasallam) never fasted in any month more than in the month of Sha'ban. He used to say, "Do those deeds which you can do easily, as Allah will not get tired (of giving rewards) till you get bored and tired (of performing religious deeds)." The most beloved prayer to the Prophet was the one that was done regularly (throughout the life) even if it were little. And whenever the Prophet (sallallaahu `alayhi wasallam) offered a prayer he used to offer it regularly .
Volume 3, Book 31, Number 192:
Narrated Ibn 'Abbas (radiallaahu `anhu):
The Prophet (sallallaahu `alayhi wasallam) never fasted a full month except the month of Ramadan, and he used to fast till one could say, "By Allah, he will never stop fasting," and he would abandon fasting till one would say, "By Allah, he will never fast."
Volume 3, Book 31, Number 193:
Narrated Anas (radiallaahu `anhu):
Allah's Apostle (sallallaahu `alayhi wasallam) used to leave fasting in a certain month till we thought that he would not fast in that month, and he used to fast in another month till we thought he would not stop fasting at all in that month. And if one wanted to see him praying at night, one could see him (in that condition), and if one wanted to see him sleeping at night, one could see him (in that condition) too.
Volume 3, Book 31, Number 194:
Narrated Humaid:
I asked Anas (radiallaahu `anhu) about the fasting of the Prophet (sallallaahu `alayhi wasallam). He said "Whenever I liked to see the Prophet (sallallaahu `alayhi wasallam) fasting in any month, I could see that, and whenever I liked to see him not fasting, I could see that too, and if I liked to see him praying in any night, I could see that, and if I liked to see him sleeping, I could see that, too." Anas (radiallaahu `anhu) further said, "I never touched silk or velvet softer than the hand of Allah's Apostle (sallallaahu `alayhi wasallam) and never smelled musk or perfumed smoke more pleasant than the smell of Allah's Apostle (sallallaahu `alayhi wasallam)."
After reading all these narrations, the one who wants to overdo fasting and praying at night (or any other form of worship), and give up all the good of this world (zuhd) needs to answer one question: Is he more righteous than the Prophet (sallallaahu `alayhi wasallam)?
Continuity and balance. These two things will take you a long way inshaAllah. Whatever little/more you do of worship, continue it. And don't overdo anything - not even worship. :)
As for the fiqh of fasting in Sha`baan, a summary has been posted here.
