Shama-il Tirmidhi Chapter 042, Hadith Number 003 (283).

Ibn 'Abbaas Radiyallahu 'Anhu relates: "Rasulullah Sallallahu 'Alayhi Wasallam fasted the major portion of the month at times, till we thought that he did not intend ending the fasts. In some months he did not fast, we began to think he would not fast now. Besides Ramadaan he did not fast for a full month".

Commentary
The practice of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam has been mentioned in many narrations. There are two reasons for this. The first one has already been mentioned in the beginning of the chapter, that in reality saum is an antidote, and at times it is a medicine for spiritual fulfilment and other benefits. In this manner according to the general rules of medicine, at times it is necessary to use medicine continuously, and at times there is no need for it, or if it is casually needed, then due to some timely obstacles it is necessary to abstain from it. This is common among physicians. Who can reach the state of a spiritual doctor more than Sayyidina Rasulullah Sallallahu 'Alayhi wasallam, therefore, Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam many a time fasted continuously for some timely necessities, and at times did not fast. The spiritual doctors of the ummah, may determine for the sake of spiritual benefit, when should one fast and when should one not fast. Those who are not spiritual doctors themselves, should consult those who are and benefit from them. The second reason is this that Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam has a few special practices. For example, the fasting on the days of Monday and Thursday; three days in every month; the ayyamul beed (i.e. the 13th 14th 15th day of the Islamic lunar month); tenth of Muharram and the tenth of Dhul Hijjah etc. Many times because of being on a journey, or due to some obstacles these fasts were not kept. When the obstacles were overcome he kept these missed fast as qadaa, and also to complete his special practices. It was also from the special habit of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam that whenever he began a devotion he continually kept up the practice. Therefore whenever any fast were missed from his special practices, he completed them by observing continuous fasts. O Allah grant us the strength to follow his noble path.