Reference: Fataawa Ramadhaan – Volume 2, Page 861, Fatwa No.846
Fiqh al-‘Ibaadaat – Page 208
Question: We would like to know what is meant by “i’tikaaf” and it’s ruling?
Response: I’tikaaf is for a person to confine himself to the masjid in obedience to Allaah (Subhaanahu wa Ta’aala) so as to separate himself from the people and free himself [from the chores of daily life] to exert himself in worshipping Allaah. This can take place in any masjid, whether it is a masjid in which people gather for the Jumu’ah prayer or not. However, it is better [to perform the i’tikaaf] in a masjid in which the people gather for the Jumu’ah prayer so that one performing i’tikaaf is not forced to leave the masjid [in which he is doing i’tikaaf] to go to another masjid for the Jumu’ah prayer.