The days of Maghfirat (forgiveness) conclude with 20th day of fasting. The third part of Holy Ramzan called 'Nazat' (salvation) begins on the 21st.
'Itikaf' is a special Ibadat and part of Sunnah of Nazat-phase. The period of Itikaf begins before the sunset of the 20th and it continues till the sighting of the moon of the month of Shawal.
The word 'Itikaf' is derived from the root 'ukuf' meaning 'to stick to something' or 'place'. 'Itikaf' means 'confining' or 'staying'. In practice, it is a retreat in the Mosque.
The 'Mutakif' (who observes Itikaf) withdraws from the worldly activities or engagements, in complete seclusion in the corner of the Mosque for purification of soul to achieve love of Allah and also to have the special blessings and mercy of Shab-e- Qadr (in one of the uneven nights). It is a complete retirement aiming at spiritual attainment.
In the 125th verse of Sura Baqara 'retreat' has been stated, "or use it (Allah's house) as a retreatt." The 187th verse of the same Sura directs the Mutakif to avoid association with wife, to remain far from sexual enjoyment : " t But do not associate with your wives while ye are in retreat in the Mosques. Those are limits (set by) Allah. Approach not nigh thereto ….."
Allama Yusuf Ali concludes his comments: "So that all carnal temptations may be avoided."
Rasulullah (SM) said: It will be of the same merit of two Hajj and two Umra for one who performs Itikaf in the last ten days of Ramzan.
Retirement from all worldly enjoyments and pleasures for Ibadat and meditation and confining oneself in the Mosque is Itikaf. It is an occasion to dedicate to spiritual quest for nearness of Allah through zikir-azkar, doa-durud and tilawat.
Observance of Itikaf is 'Sunnat-e-Muakkada Kefaya.' 'Kefaya' demands: If some people of a locality in a Mosque observe it, this will do. But if none observes, all will be sinners for deviation.
According to Hadith, it is better for women to confine themselves in the corner of their house and dedicate in rituals where they offer prayer.