It was narrated from Abu Salamah that ‘Aa’ishah (may Allaah be pleased with her) said: The Prophet (peace and blessings of Allaah be upon him) did not fast in any month more than Sha’baan, and he used to fast all of Sha’baan and he used to say: “Do as much of good deeds as you can, for Allaah does not get tired (of giving reward) until you get tired.” And the most beloved of prayers to the Prophet (peace and blessings of Allaah be upon him) was that in which one persists even if it is little. When he offered a prayer he would persist in doing so.
Narrated by al-Bukhaari, 1869; Muslim, 782.
Ahmad (26022), Abu Dawood (2336), al-Nasaa’i (2175) and Ibn Maajah (1648) narrated that Umm Salamah (may Allaah be pleased with her) said: “I never saw the Messenger of Allaah (peace and blessings of Allaah be upon him) fast two consecutive months apart from the fact that he used to join Sha’baan and Ramadaan.”
If it is asked, what is the reason for fasting a great deal during Sha’baan? The answer is:
The reason in explained in the report narrated by al-Nasaa’i and Abu Dawood, and classed as saheeh by Ibn Khuzaymah, according to which Usaamah ibn Zayd said: “I said, ‘O Messenger of Allaah, I do not see you fasting in any month more than in Sha’baan.’ He said, ‘That is a month concerning which many people are heedless, between Rajab and Ramadaan. It is the month is which people’s deeds are taken up to the Lord of the Worlds, and I would like my deeds to be taken up whilst I am fasting.’” Classed as hasan by al-Albaani in Saheeh al-Nasaa’i, 2221.
And Allaah knows best.
– Taken from Islam-QA.