Hiban bin Hilal حبان بن هلال · The Book of Fasting

"When you see the crescent then fast, and when you crescent then fast, and when you see it, stop fasting. If it is obscured from you (too cloudy), then fast thirty days."

"The Messenger of Allah mentioned the crescent and said: 'When you see it, fast and when you see it, stop fasting, and if it is obscured from you (too cloudy), then count thirty days."'

'Uthman bin Abi Al-As called for milk to be given to him (Mutarrif) to drink. Mutarrif said: 'I heard the Messenger of Allah say: 'Fasting is a shield like the shield of any one of you in battle."' Abu Hurairah said: "The Messenger of Allah said: 'Fasting is a shield."' (Sahih

That he came to Prophet, and he mentioned something similar.

"Whoever does not intend to fast before dawn comes, should not fast." (Daif)

"The Messenger of Allah enjoyed three things upon me: To sleep after praying Witr, to perform Ghusal on Friday, and to fast three days of each month." (Sahih).

"There are four things which the Prophet never gave up: Fasting 'Ashura', (fasting during) the ten days, (fasting) three days of each month, and praying two Rak'ahs before Al-Ghadah (Fajr)."

That the Prophet commanded a man to fast on the thirteenth, fourteenth and fifteenth.

"Ubayy said: 'A Bedouin came to the Messenger of Allah, and he had a rabbit that he had grilled and some bread. He placed it before the Prophet then he said: "I found it bleeding." The Messenger of Allah said to his Companions: "It doesn't matter; eat." And he said to the Bedouin: "Eat," He said: "I am fasting." He said: "If you want to fast then you should fast the shining days of Al-Bid: The thirteenth, fourteenth and fifteenth."