1) the legal/technical meaning of al-i'tikaaf: it is the confining (of oneself) to the masjid and remaining there with the intention of worshipping allah (alone).
2) the legislation of al-i'tikaaf: the scholars are in agreement as to the legality of al-i'tikaaf:
((because the prophet (peace be upon him) used to perform i'tikaaf during the last ten (days and nights) of ramadan right up until his death, then his wives performed i'tikaaf after him.)), [the authenticity of this narration has been agreed upon by al-bukhaaree and muslim]
3) the divisions of i'tikaaf: i'tikaaf is divided into that which is recommended and that which is obligatory. as for the recommended, then it is that which the muslim performs according to the example of the messenger (peace be upon him) during the final ten days and nights of ramadan.
the obligatory i'tikaaf is that which a person has made obligatory upon himself by way of undertaking an oath to do so.
4) the specified time for the i'tikaaf:
((when the prophet (peace be upon him) intended to perform the i'tikaaf, he would perform the fajr prayer [i.e. on the morning of the 20th day of ramadan], then enter the place where he planned to remain during the i'tikaaf)), [the authenticity of this narration has been agreed upon by al-bukhaaree and muslim]
5) the conditions of the one performing the i'tkaaf: that he/she be a muslim, fully aware of his/her faculties, pure from any state of impurity such as janaabah (state of major ritual impurity, i.e. after having had sexual relations), menses and post-partum bleeding.
6) the pillars of i'tikaaf: to confine oneself to the masjid (for a specified time) with the intention of worshipping allah.
7) that which is permissible for the person performing the i'tikaaf: the following is permissible for the person performing i'tikaaf:
a) combing his hair, shaving his head, cutting his nails, maintaining the cleanliness of his body, perfuming himself and wearing the best of garments;
b) leaving (the masjid) for an absolute necessity, such as (answering the call of nature by) urinating and passing stools, and eating and drinking if he is unable to find someone to cater for him.
c) it is required of the person performing the i'tikaaf that he eat, drink and sleep in the masjid making sure to keep it clean.
8) the etiquettes of i'tikaaf: on the authority of 'aa.ishah (radhi-yallahu 'anhaa) who said:
((the (established) sunnah for the one performing i'tikaaf is that he not visit the sick, nor follow the funeral procession, nor touch or have intercourse with a woman, nor leave (the masjid) except for an absolute necessity; and i'tikaaf is not to be performed except whilst fasting, nor except in the masjid where the jumu'ah prayer is performed.)),
[saheeh, transmitted by al-bayhaqee and abu daawood]
9) that which nullifies the i'tikaaf:
a) intentionally leaving the masjid for other than an absolute necessity;
b) mental instability;
e) post partum bleeding.