THE FASTING CHAPTER · 60 – FASTING ON MONDAYS AND THURSDAYS: THE GATE
It is narrated from al-Hakam, the freedman of Usamah ibn Zayd:
I accompanied Usamah to Wadi al-Qura intending to ask him about something pertaining to his property.
Usamah used to fast on Mondays and Thursdays. His freedman said to him, “You are an elderly man, why do you fast on Mondays and Thursdays?” Usamah replied, "The Messenger of Allah, peace be upon him, used to fast on Mondays and Thursdays.” When he was asked why he fasted those days, the Messenger of Allah, peace be upon him, answered, “Because the deeds of servants are presented [to Allah] on Mondays and Thursdays." (So I observe them because of that.)