Shama-il Tirmidhi Chapter 42, Hadith Number 13 (293).

‘Alqamah Radhiyallahu anhu relates: “I asked Aayeshah Radhiyallahu anha: ‘Did Rasulullah Sallallahu ‘Alayhi Wasallam fix a day for ‘Ibaadah? She replied: ‘The practices of Rasulullah Sallallahu ‘Alayhi Wasallam was of a continuous nature. Who among you have the strength, which Rasulullah Sallallahu ‘Alayhi Wasallam had?'”

That meant to set aside a day for some special devotion. For example, to specify Monday for fasting. Fast is observed on every Monday and nothing is ever eaten on this day. Or besides Monday, fast are not observed on other days. Both these were not found, but it was certainly the practice of Sayidina Rasulullah Sallallahu ‘Alayhi Wasallam that, whatever deed he began observing, he punctually continued its practice. You do not possess the strength and cannot fulfil these with such punctuality as that of Rasulullah Sallallahu ‘Alayhi Wasallam’. He punctually completed his prescribed practices. If for any reason it could not be fulfilled, he completed it at a later time, as has been mentioned in the fasts of Sha’baan. The gist of this is, that it was not given such importance that, the deed was observed only on a particular day, and no other deed was observed on that day. He certainly fulfilled his prescribed practices with care among which are included the fasting on special days. No doubt remains on this commentary, that Sayyiditina ‘Aayeshah Radiyallahu ‘Anha, has mentioned in hadith number eight, that special attention was given to the fasting on Mondays and Thursdays. The findings of Haafizul Hadith (one who has memorised a minimum of 100 000 ahaadith with its chain of narrators), Ibn Hajar RA is that this question and answer is regarding these three fasts, it was the practice of Sayyidina Rasulullah Sallallahu ‘Alayhi Wasallam to observe these fasts every month. This has already been mentioned in hadith number seven. According to this explanation there is no confusion.