The scholars differed as to the reasons why the Prophet (blessings and peace of Allah be upon him) fasted so much in Sha'ban. Their various opinions are as follows: That he had been unable to fast three days out of every month because he was travelling or for some other reason, so he made them all up together in Sha'ban.
When the Prophet (blessings and peace of Allah be upon him) began to do some voluntary action, he would persist in it, and if he missed it, he would make it up later. It was said that his wives used to make up the days that they missed of Ramadan in Sha'ban, so he used to fast because of that. This is the opposite of what was reported from ‘Aishah, may Allah be pleased with her, that she used to delay making up days that she had missed in Ramadan until Sha'ban because she was too busy with the Messenger of Allah (blessings and peace of Allah be upon him) to fast. It was said that it was because this is a month which people do not pay attention to.
This is the most correct view, because of the Hadith of Usamah, may Allah be pleased with him, quoted above, in which it says: “That is a month to which people do not pay attention, between Rajab and Ramadan.” (Reported by an-Nasai, see Sahih at-Targhib wat-Tarhib, p. 425)
When Sha'ban began, if the Prophet still had some voluntary fasts outstanding that he had not fasted, he would make them up during Sha'ban so that his voluntary fasts would be complete before Ramadan came. Similarly, if he had missed some Sunnah prayers or he had missed Qiyam al-Layl, he would make it up.
‘Aishah, may Allah be pleased with her, used to make the most of this opportunity to make up any obligatory Ramadan fasts that she had missed because of menstruation; during other months she was too busy with the Prophet (blessings and peace of Allah be upon him) to fast. We should also note here that anyone who has any missed fasts to make up has to make them up before the next Ramadan comes. It is not permissible to delay it until after the following Ramadan except in cases of necessity (such as a valid excuse that continues between the two Ramadans).
Whoever is able to make them up before the (second) Ramadan and does not do so, has to make them up after the (second) Ramadan and in addition to that, he has to repent and to feed one poor person for each day that he missed. This is the view of Malik, ash-Shafi’i and Ahmad. Another benefit of fasting in Sha'ban is that it is a kind of training for the Ramadan fast, in case a person finds it difficult to fast when Ramadan starts; if he fasts in Sha'ban he will have gotten used to fasting and he will feel strong and energetic when Ramadan comes.
Sha'ban is like an introduction to Ramadan and it has some things in common with Ramadan, such as fasting, reciting Quran and giving in charity. Salamah ibn Suhayl, may Allah have mercy on him, used to say: “The month of Sha'ban is the month of reciters (of the Quran).” Habib ibn Abu Thabut, may Allah have mercy on him, used to say, when Sha'ban came: “This is the month of reciters (of the Quran).” When Sha'ban came, ‘Amr ibn Qays al-Mala’I, may Allah have mercy on him, used to close his store and devote his time to reading the Quran.