Abdullah bin Sa'id bin Abi Hind عبد الله بن سعيد بن أبي هند · The Book of Fasting

"Al-Hakam said to me: 'I heard it from him forty years age; Then Al-Hakam said: 'And Maimum bin Abi Shabib narrated it to me from Muadh bin Jabal." (Sahih

"The Messenger of Allah commanded me to sleep after praying Witr, to perform Ghusl on Friday and to fast three days of each month." (Sahih).