We kept fast for twenty-nine days along with the Prophet (ﷺ) more often than we kept fast for thirty days.
Sunan Abi Dawud Book 14, Hadith 10
← Previous Hadith 'Umar b. 'Abd al-'Aziz wrote (a letter) to the people of Basrah: It has reached us from the Messenger of Allah (ﷺ), like the tradition narrated by Ibn 'Umar from the Prophet (ﷺ). This version adds: The best calculation is that when we sight the moon of Sha'ban on such-and-such date, fasting will being on such-and-such dates, Allah willing, except they they sight the moon before that (date).

Sunan Abi Dawud Book 14, Hadith 9 Next Hadith → The Prophet (ﷺ) as saying: The two months of 'Id (festival), Ramadan and Dhu al-Hijjah, are not defective.

Sunan Abi Dawud Book 14, Hadith 11