Iʿtikāf

Iʿtikāf (Arabic: اعتكاف‎‎, also i'tikaaf or e'tikaaf) is an Islamic practice consisting of a period of staying in a mosque for a certain number of days, devoting oneself to ibadah during these days and staying away from worldly affairs. The literal meaning of the word suggests sticking and adhering to, or being regular in, something, this 'something' often including performing nafl prayers, reciting the Qur'an, and reading hadith.

Some Muslims claim that a performance of i'tikāf to a beggar sitting outside another's house, knowing that with persistence the occupant of the house will apparently give something to help. Others may claim that one can more easily identify when Ramadan's night of power will occur.

It is considered sunnah to perform i'tikāf for ten full days, these ten often being the last of the month of Ramadan; any ten consecutive days, however, may be chosen. I'tikāf may also be observed for three full days, often the 13th through the 15th of Ramadan, or for a full day from sunset to sunset, in each case supererogatorily. The shortest i'tikāf, also considered supererogatory, can be observed for the duration of time between two daily prayers (such as from Asr to Maghrib).

Because in every case except for the last, one ought to be fasting at the same time, performing i'tikāf on Eid al-Fitr or Eid al-Adha would not be permissible.

A person who wishes to take part in i'tikāf (a mu'takif) must be a sane and clean Muslim, not causing strife within the family in taking part, and unambiguously in the main masjid of the person's town or city (not any other place of congregation, though exceptions may be made in extraneous circumstances). The person must make the appropriate intention, either on the person's own behalf or on behalf of someone else unable to do so, to commit to staying inside the masjid for the entire period chosen for i'tikāf, except for very important or unavoidable reasons (such as buying food or attending a funeral). This intention must be made on the sunset prior to the first day of i'tikāf.

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Wikipedia