Dear questioner, thank you very much for your very important question.

You are inquiring about an Islamic ritual called I`tikaf. Linguistically, I`tikaf means to engage and to devote something to a thing, be it good or bad. In Shari’ah it means to engage in a retreat in the Masjid and stay there with the intention of seeking nearness to Allah the Almighty, and His reward.

Its legalization

The majority of Muslim scholars agree that I`tikaf is permissible, for the Messenger of Allah (peace be upon him) observed I`tikaf in the month of Ramadan during the last ten days. In his last Ramadan he observed it 20 days, as is related by Bukhari and others. Besides, his companions and wives observed it during his lifetime and after.

The prerequisites of I`tikaf

For a retreat to be valid, the observer must be Muslim, must have reached puberty, and must be pure from janabah (major defilement, menstruation, and post-childbirth bleeding).

The pillars of I`tikaf

There are two pillars for I`tikaf: intention, and staying in the Masjid. Allah states:

But do not associate with your wives while you are in retreat in the masajid… (Al-Baqarah 2:187)

This verse prohibits two things: marital relationships during I`tikaf because this contradicts the spirit of devotion, and observing I`tikaf in any place but a masjid. Thus, any believer, man or woman, who desires to observe I`tikaf may do so only in a masjid as we see the Messenger (peace be upon him)’s wives were building their tents in the masjid.

What a person in I`tikaf should engage in

It is recommended that the person in a state of I`tikaf should engage in supererogatory worship, and engage himself with prayer, recitation of the Qur'an, Glorification of Allah, Praising Allah, frequent declaration of the testimony of faith, Takbir (saying Allahu-Akbar “Allah is the Greatest”), seeking forgiveness from Allah, invoking Allah’s blessing on the Messenger of Allah (peace be upon him), and supplications, as well as any act of worship that will bring the servant nearer to Allah.

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Source: Taken with modifications from “Ramadan the Fasting Month” by Tajuddin B. Shuaib