al-Qasim bin Zakaria bin Dinar القاسم بن زكريا بن دينار القرشي · The Book of Fasting

"Do you have anything this morning that you can give me to eat?" we would say no, and he would say: "I am fasting." Then after that he came and she said: "I have been given a gift." He said: "What is it?" she said: "Hais." He said: "I started the day fasting," but then he ate.

"The Messenger of Allah used to be keen to fast on Mondays and Thursday."