By Language (Lughah):
- الملازم - follow, accompany, familiarize, honor (See Imam ash Syaukani, Fathul Qadir, 1 / 244. Mawqi 'Ruh al-Islam)
يقال عكف على الشيء: إذا لازمه
It says, 'akafa' ala Ash Syai '(He settled on something), meaning he was always with him. (Ibid)
Shaykh Sayyid Sabiq rahimahullah says:
الاعتكاف لزوم الشئ وحبس النفس عليه, خيرا كان أم شرا
I'tikaf is to honor something and shut down, in terms of good or bad. (Fiqhus Sunnah, 1 / 475)
In term (Personality '):
والاعتكاف في الشرع: ملازمة طاعة مخصوصة على شرط مخصوص
In Personality ': settled in order to adhere specifically to the special requirements as well. (Fathl Qadir, 1 / 245)
Shaykh Sayyid Sabiq rahimahullah says:
والمقصود به هنا لزوم المسجد والاقامة فيه بنية التقرب إلى الله عزوجل.
What is meant here is I'tikaf fulfill prayers in mosques and enforce it with the intention of drawing nearer to Allah 'Azza wa Jalla. (Fiqhus Sunnah, 1 / 475)
Legal Basis
- Koran
ولا تباشروهن وأنتم عاكفون في المساجد
Do not you interfere with them (wife), while you're I'tikaf at the mosque. (Surat al-Baqara: 187)
- As Sunnah
Of 'Aisha radiallahu' anha:
أن النبي صلى الله عليه وسلم كان يعتكف العشر الأواخر من رمضان حتى توفاه الله ثم اعتكف أزواجه من بعده
That the Prophet sallallaahu 'Alaihi wa Sallam retreat in the last 10 days of Ramadan till he diwafatka God, then his wives were I'tikaf after that. (Narrated by Bukhari, No. 2026, No. Muslims. 1171, Abu Daud No. 2462. Ahmad No. 24 613, and others)
From Abu Hurayrah, he said:
كان النبي صلى الله عليه وسلم يعتكف في كل رمضان عشرة أيام فلما كان العام الذي قبض فيه اعتكف عشرين يوما
Formerly the Prophet sallallaahu 'Alaihi wa Sallam I'tikaf in every 10 days of Ramadan, when in the year he died, he I'tikaf 20 days. (Narrated by Bukhari No. 694, No. Ahmad. 8662, Ibn Hibban No. 2228, Al Baghawi No. 839, Abu Ya'la No. 5843, Abu Nu'aim in Akhbar Ashbahan, 2 / 53)