Fasting (Kitab Al-Siyam)

Dawud :: Book 13 : Hadith 2457

Narrated Ubayy ibn Ka'b:

The Prophet (peace_be_upon_him) 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).