Abu Hurairah reported that the most the Prophet would fast would be Monday and Thursday. He was asked about that and he said: “The actions are presented on every Monday and Thursday. Allah forgives every Muslim or every believer, except for those who are boycotting each other. He says [about them]: ‘Leave them.'” This is related by Ahmad with a sahih chain. It is recorded in Sahih Muslim that the Prophet, when asked about fasting on Monday, said: “That is the day on which I was born and the day on which I received revelations.”
Section : Fasting Mondays and Thursdays.