Thabit bin Aslam Albanani ثابت بن أسلم البناني · Fasting (Kitab Al-Siyam)

The Prophet (ﷺ) said: Do not fast one day or two days just before Ramadan except in the case of a man who has been in the habit or observing a fast (on that day); and do not fast until you sight it (the moon). Then fast until you sight it. If a cloud appears on that day (i.e. 29th of Ramadan) then complete the number thirty (days) and then end the fasting: a month consists of twenty-nine days.

The Prophet (ﷺ) said: When one of you is fasting, he should break his fast with dates; but if he cannot get any, then (he should break his fast) with water, for water is purifying.

A man from the Companions of the Prophet (ﷺ) told me that the Messenger of Allah (ﷺ) prohibited cupping and perpetual fasting, but he had not made them unlawful showing mercy on his Companions. Thereupon he was asked: Messenger of Allah, you observe perpetual fast till dawn. He replied: I observe perpetual fast till dawn (for) my Lord gives me food and drink.

The Prophet (ﷺ) used to observe retirement (i'tikaf) to the mosque during the last ten days of Ramadan till Allah took him, and then his wives observed retirement to the mosque after his death.