1؎ : This hadith indicates that the Prophet (sallallahu alayhi wa sallam) instructed to repeat (observe) fasting on Monday, and previously a hadith has been mentioned in which he used to repeat (observe) fasting on Thursday. By combining both narrations, it is understood that what is required is to fast three days among these two days, whether by repeating on Monday or on Thursday. And Allah knows best.
Explanation & Benefits
Hafiz Muhammad Ameen
(1) "He used to command." That is, as a recommendation (mustahabb). (2) "The first Thursday." In previous narrations, mention is made of the first Monday. The intent is that if the first Thursday arrived, then he would fast on Thursday, Monday, and then the next Monday; and if Monday came first at the beginning of the month, then he would fast on Monday, Thursday, and then the following Thursday. That is, the three fasts would be confined to Mondays and Thursdays. Whether the beginning is from Thursday or Monday, there is no difference.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 2421