Nasai

Apparently, from this narration it seems that the Messenger of Allah (sallallahu alayhi wa sallam) used to fast the entire month of Sha'ban, but this is not correct; rather, he (sallallahu alayhi wa sallam) would leave out fasting for a few days towards the end. This clarification is coming ahead in hadith number 2179 and 2180. Since he (sallallahu alayhi wa sallam) used to fast most of the days, it was thus stated that he fasted the whole month. In customary speech, the rule is that the majority is referred to as the whole (lil-akthar hukm al-kull), and this becomes common in conversation.

Commentary in English:
The narrations regarding fasting in Sha'ban have already been mentioned previously. If those narrations and this narration are considered together, it becomes apparent that both possibilities exist: that there was diversity in the practice of the Messenger of Allah (sallallahu alayhi wa sallam)—sometimes he would fast the entire month of Sha'ban, and in some years he would not fast the whole month but would fast most of it. The aforementioned hadith of Umm Salamah (radi Allahu anha) supports this reconciliation. In summary, reconciliation (tatbiq) is better than giving preference (tarjih), as this allows both types of hadith to be acted upon. And Allah knows best.

Benefits and Issues:
The statement of Umm Salamah radi Allahu anha is figurative (majaz).
Its meaning is abundance.
As in other hadiths, it is mentioned that the Prophet sallallahu alayhi wa sallam used to fast abundantly in Sha'ban.
In Sahih Muslim, there is a narration from Aisha radi Allahu anha: (He used to fast in Sha'ban except for a little) (Sahih Muslim, al-Siyam, Hadith: 1156)