Bismillah.
Volume 3, Book 33, Number 248:
Narrated Ibn 'Umar (radiallaahu `anhu):
Umar (radiallaahu `anhu) asked the Prophet (sallallaahu `alayhi wasallam) "I vowed in the Pre-lslamic period of ignorance to stay in Itikaf for one night in Al-Masjid al-Haram." The Prophet (sallallaahu `alayhi wasallam) said to him, "Fulfill your vow."
There are three main types of I`tikaaf:
- WAJIB: To vow or pledge to make I'tikaaf (on a fixed day) for the sake of Allah upon the fulfilment of some wish or desire.
- SUNNAT-MUAKKADAH: To reside the last ten nights and days of Ramadhan in the Masjid is Sunnat-Muakkadah, i.e. If a person from the community fulfills the obligation of I'tikaaf, the entire community will be absolved of this sacred duty. Otherwise all the residents will be sinful of neglecting this Sunnah.
- MUSTAHAB OR NAFL: This I'tikaaf can be for any amount of time, even for a few minutes.
