Shama-il Tirmidhi Chapter 042, Hadith Number 004 (284).

Ummi Salaah Radiyallahu 'Anha reports: "I did not observe Rasulullah Sallallahu 'Alayhi Wasallam fast for two consecutive months, besides the month of Sha'baan and Ramadhaan".

Commentary
Apparently this hadith seems to contradict all the previous ahaadith. Till now all the ahaadith were unanimous that besides Ramadhaan Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam did not fast for a complete month. In this hadith the month of Sha'baan has also been added. The 'ulama have reconciled both in many ways. The first is that in this hadith the whole of Sha'baan is mentioned as an exaggeration. The noble habit of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam was to fast for most part of the month. This has accordingly been made clear in a hadith from Sayyiditina Aayeshah Radiyallahu 'Anha which will be mentioned in the ensuing hadith. The second is that it may be possible, at some time Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam by chance kept fast for the whole month of Sha'baan, the news of which reached Sayyiditina Ummi Salamah Radiyallahu 'Anha and did not reach the others. The third is that in the narrations of Sayyiditina Aayesha Radiyallahu 'Anha, Sayyidina Ibn Abbas Radiyallahu 'Anhu, and others, the habit of doing so is denied, that Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam did not fast for consecutive days in any month besides that of Ramadhaan. It will not contradict this statement if by chance fasts are kept for the full period of any other month. Therefore if for some reason Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam fasted for the whole month of Sha'baan in some year, -and since this was not his normal practice, -for this reason Sayyiditina 'Aayeshah Radiyallahu 'Anha and others did not mention it, and Sayyiditina Ummi Salamah Radiyallahu 'Anha mentioned he did, because he fasted for the whole month. There is no contradiction here. The fourth explanation is that in the beginning Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam fasted for the whole month of Sha'baan and in the later years because of weakness, lessened the amount of days. Therefore, whoever mentions the later deeds, said this because it was towards the end, and said he fasted for most of the month. The one that thought that this was because of some reason or obstacle, says the original practice was to fast for the whole month. Some are of the opinion that it is the opposite, in the beginning he fasted for most of the month and in later days he began fasting for the full month.