Do not observe fast for a day, or two days ahead of Ramadan except a person who is in the habit of observing a particular fast; he may fast on that day.
Sahih Muslim Book 13, Hadith 24
← Previous Hadith Observe fast when you see it (the new moon) and break fast when you see it (the new moon of Shawwal), but when (the actual position of the month is) concealed from you (on account of cloudy sky), then count thirty days.

Sahih Muslim Book 13, Hadith 23 Next Hadith → This hadith has been narrated on the authority of Yahya b. Abi Kathir with the same chain of transmitters.

Sahih Muslim Book 13, Hadith 25