Is it forbidden to fast during the second half of Sha’ban, and was this mentioned in "Riyad al-Salihin"?

The statements of the scholars regarding the ruling on commencing fasting in the second half of Sha'ban can be summarized into four opinions:

1. Absolute permissibility: Whether one fasts the entire second half, or separates it with a break in fasting, or singles out the 'Day of Doubt' (Yawm al-Shakk). 2. No harm in fasting the Day of Doubt voluntarily: This is the opinion of Malik and Ibn Abd al-Barr. 3. Impermissibility: Unless one connects their fasting with some of the first half (of Sha'ban), or it coincides with a habitual fast. This is the sounder opinion among the Shafi'is. 4. Only the Day of Doubt is forbidden: Other days in the second half are not forbidden.

It is possible to reconcile the hadiths that prohibit fasting in the second half of Sha'ban with those that permit it by interpreting the prohibition as applying to those who do not have a habit of fasting at that time, and the permission as applying to those who do have a habit.

Among the hadiths reported concerning this are: "When half of Sha'ban remains, do not fast," and "None of you should precede Ramadan with a fast of one or two days, unless a man has a habitual fast which he observes, in which case he may fast that day." Also, the statement of Aisha, may Allah be pleased with her: "He (the Prophet) used to fast all of Sha'ban until he connected it with Ramadan."