Yahya bin Sa'id al-Ansari يحيى بن سعيد الأنصاري · Fasting (Kitab Al-Siyam)

A man came to the Prophet (ﷺ) and said: Messenger of Allah, I ate and drank in forgetfulness when I was fasting. Hie said: Allah had fed you and given you drink.

The Prophet (ﷺ) used to observe i'tikaf during the last ten days of Ramadan. One year he did not observe i'tikaf. When the next year came, he observed i'tikaf for twenty nights (i.e. days).