Abu Karayb, Muhammad bin al-'Ala' محمد بن العلاء - أبو كريب · The Book on Fasting

the Prophet said: "Do not precede the month with a day nor with two days, unless that fast falls on a day that one of you would have (normally) fasted. Fast with its sighting and break fast with its sighting, and if it is cloudy, then count for thirty days, and then break (the fast)."

"Some cavalry man of the Messenger of Allah came galloping upon us, so I came to the Messenger of Allah and found him having lunch. He said: "Come and eat." I said: 'I am fasting.' So he said: 'Come and I will narrate to you about the fast - or fasting. Indeed Allah Most High lifted (the fast and) half of the Salat from the traveler, and (He lifted) the fast - or fasting - from the pregnant person, or…

(A Hadith similar to no. 716 with a different chain.)

"I met up with Ibn Abbas while he was reclining on his Rida at the Zamzam (well). So I said: 'Inform me about the Day of Ashura. On which day is it fasted?' He said: 'When you see the crescent of Al-Muharram, then count, then fast on the morning of the ninth day.'" He said: 'I said: Is this how Muhammad fasted it?' He said: 'Yes.'"