Literally, E'tikaf (cleave to a mosque) means to stay or remain at a place or to cleave to smething. E'tikaf in Islamic law is a pious practice consisting of a period of retreat at a sacred place for the purpose of seeking proximity and nearness to God, the Exalted. E'tikaf is not particular to Islam because it had also been practiced by other religions before it. Thus, Islam has simply carried on this act of worship, though some of its features and rules may have changed in the sacred Shari'ah of Islam. The time for this form of worship could be anytime when one is allowed to fast. Hence, whenever one can observe fast, he can observe E'tikaf as well. The best time is the month of Ramadan, especially the last ten days of this month. Also, it is recommended to observe E'tikaf duing Ayyamul Beidh (days of bright nights) of the month of Rajab. According to the verdict of some jurists, a person should stay in one of the following mosques for performing E'tikaf: Masjid-ul-Haram (in Makkah); Masjid-un-Nabi (the Mosque of the Prophet (P.B.U.H.) in Madinah); Mosque of Kufa; Mosque of Basra. However, some other jurists have said that it is permissible to perform E'tikaf in the central mosque of every city or region.
Literally, E'tikaf means to stay or remain at a place or to cleave to something. E'tikaf in Islamic law is a pious practice consisting of a period of retreat at a sacred place for the purpose of seeking proximity and nearness to God, the Exalted.
E'tikaf is a very good opportunity for an individual who is lost in the transient and earthly pleasures of this world to redeem himself and to detach from physical desires which last but a few days. Thus, he who observes E'tikaf should surrender himself to God and ask Him to keep him steadfast on the right path so that he may benefit from the unfathomable and endless ocean of divine grace, bounty, forgiveness and blessing.
E'tikaf is not particular to Islam because it had also been practiced by other religions before it. Thus, Islam has simply carried on this act of worship, though some of its features and rules may have changed in the sacred Shari'ah of Islam.
Ever since the Prophet of Islam (s) taught Muslims E'tikaf, this pious practice has become prevalent among Muslims. At present, E'tikaf is held during the last ten days of Ramadhan in many Islamic countries including Saudi Arabia (Mecca). Each year tens of thousands of Muslims from across the world rush to Mecca and retreat therein for devotion. There are many pilgrims of the House of God who in order to attain the virtues of E'tikaf during the last ten days of Ramadhan choose to do their Umrah pilgrimage during these days.
Similar ceremonies have been held in Masjid al-Nabi near the sacred shrine of the Holy Prophet (s). The Mosque of Kufa in Iraq is also another place where E'tikaf has been held for many years especially during the last ten days of Ramadhan. A great many Shiites and followers of the Ahlul-Bait (a) have been gathering in this sacred mosque with many great Shiite scholars joining people in this ceremony.
The Spiritual Value of E'tikaf
Breaking off with the worldly affairs, confining oneself to the mosque, and continuous zikr and worship of Allah are highly valuable and important by themselves even if they are not in the form of E'tikaf. There are many verses and traditions bearing such a concept. However, E'tikaf has been specifically underlined and emphasized upon in the Quran. God, the Exalted, says in the Quran:
"And We enjoined Ibrahim and Ismail saying: Purify My House for those who visit (it) and those who abide (in it) for devotion and those who bow down (and) those who prostrate themselves."
Some of the conditions of E'tikaf have been mentioned in the Quran.
Time of E'tikaf
The time for this form of worship could be anytime when one is allowed to fast. Hence, whenever one can observe fast, he can observe E'tikaf as well. The best time is the month of Ramadan, especially, the last ten days. Also, it is recommended to observe E'tikaf duing Ayamul Beidh of the month of Rajab. E'tikaf during the last ten days of Ramadhan may have some link with one's becoming prepared for the Night of Qadr (destiny) so as to benefit from the blessings of this night as much as one can.
What has been mentioned in the traditions is that the Prophet (s) retreated in the mosque during the last ten days of Ramadhan. Even in the year in which he had gone to the Battle of Badr during the month of Ramadhan, he made up the missed E'tikaf in Ramadhan of the next year. So, he engaged in E'tikaf for two third of the month of Ramadhan. In Iran, E'tikaf is observed during three days of the month of Rajab with a greater number of people than in the month of Ramadhan. These three days are important from several reasons:
Firstly, Rajab is one of the haram months and it is inferred from the traditions that there are more spiritual rewards in E'tikaf in haram months than there are in other months.
Secondly, fasting in the month of Rajab has a special virtue because Rajab is a great month which people respected even in the time of ignorance. Islam further sanctified it.  It appears that such a behavior and belief towards the month of Rajab has been passed on to Muslims from other divine religions.
Place of E'tikaf
E'tikaf should be performed in special places. According to the most well-known verdict, E'tikaf should be observed in one of the following mosques: Masjid-ul-Haram (in Makkah); Masjid-un-Nabi (the Mosque of the Prophet (P.B.U.H.) in Madinah); Mosque of Kufa; Mosque of Basra. Imam Reza (a) said:
«اعتکاف لیلة فی مسجد الرسول و عند قبره یعدل حجة و عمرة»
"One night of E'tikaf in the Prophet's Mosque and near his grave amounts to one obligatory Hajj and one Umrah."
However, some other jurists have said that it is permissible to perform E'tikaf in the central mosque of every city or region. There is no doubt that he who wants to observe E'tikaf in the central mosque of a city should do so with the hope that it is desirable and that God, the Exalted, may reward him for it. It should be noted that there are only few jurists who consider E'tikaf as permissible in the mosque of a bazaar or a neighborhood. As for the central mosque, it refers to the mosque in which a greater number of people gather for prayers and acts of worship. In other words, it is a mosque which most often has more worshippers than any other mosques in the same city or area.
A question may arise here and that is: Is it not better to consider E'tikaf as permissible in every mosque because of its constructive spiritual impacts? In addition, if it is allowed to be performed in every mosque, everyone would be able to benefit from this act of worship.
It should be said in answer to the above question that the acts of worship and their special features and rules are extracted from Islamic sources and religious laws and that they should be performed in the same manner as prescribed. If it is understood from the sources that the place of E'tikaf is the central mosque, one cannot use his own taste to change the condition for an act of worship and expand its sphere.
Basically, some of the acts of worship are confined to special places and locations. For example, the rituals of hajj should be performed at certain places. Hence, it is not permissible to perform those rituals at any other places.
When it comes to E'tikaf, if it is understood from reliable Islamic sources that it can be performed in the central mosques, we come to know that God wants us to perform them at these places. There is no doubt that there are some rationales behind it which we are unaware of and our mind cannot perceive. Perhaps, Islam has restricted it to the central mosque so that He may have some control over its quantity and quality and that in addition to this act of worship, Muslim may further become united.  - 
 - Baqara (2): 125
 - Baqara (2): 187
 - Hurr Ameli, Muhammad bin Hasan Wasail al-Shi'ah, vol.10, p.533, hadith No.14046, Aalulbayt Institute, Qom 1409 A.H.
 - Ibid, hadith No. 14047.
 - Shaykh Saduq, Fadhail al-Ashhor al-Thalatha, pg.24, narration No.12.
 - Behar al-Anwar, vol.90, pg.151.
 - Sayyid Muhammad Kazemi Tabatabai, Al-Urwatul Wuthqa, Kitabl al-E'tikaf, pg.399.
 - Imam Khomeini (r), Tahrirul Wasilah, vol.1, pg.305.
 - Shaykh Muhammad Hasan Najafi, Jawaher al-Kalam, vol.17, pg.170.
 - Ibid, pg.171.
 - Ayatollah Gulpaigani, Majma'ul Masail, vol.1, pg.154.
 - Behar al-Anwar, vol.33, pg.542
 - Ismail Nassaji Zawwara, extracted from Hawzah website.