Shama-il Tirmidhi Chapter 042, Hadith Number 001 (281).

'Abdullah bin Shaqeeq Radhiyallahu 'Anhu reports: "I inquired from 'Aayeshah Radhiyallahu 'Anha regarding the (nafil) saum of Rasulullah Sallallahu 'Alayhi Wasallam. She replied: 'At times Rasulullah Sallallahu 'Alayhi Wasallam fasted continuously. We used to say, he will keep on fasting (this month). At times he did not fast, till we began thinking he will not fast (that month). Rasulullah Sallallahu 'Alayhi Wasallam did not fast for a month after he came to Madinah, besides the fasts of Ramadhaan'". (In this manner, the passing of the whole month without fasting was not observed. As mentioned in Abu Daawud. This practice of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam will be mentioned in the commentary of hadith number three in detail).