Fasting on Mondays

it was narrated that ‘Aa’ishah said: “The Messenger of Allaah محمد صلى الله عليه وسلم was keen to fast on Mondays and Thursdays.” 
(al-Nasaa’i, 2320; classed as saheeh by al-Albaani in Saheeh al-Jaami’ al-Sagheer, 4827).


The Prophet محمد صلى الله عليه وسلم was asked about fasting on Mondays and Thursdays, and he said: “Those are two days on which people’s deeds are shown to the Lord of the Worlds, and I want my deeds to be shown to Him when I am fasting.” 
(al-Nasaa’i, 2358; Ibn Maajah, 1740; Ahmad, 8161; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 1583). 


He محمد صلى الله عليه وسلم was asked about fasting on Mondays and he said, “On that day I was born and on that day revelation came to me.” (Muslim, 1162).