Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.149A.
Section : I’tikaf, the condition for i’tikaf.
The one who preforms i’tikaf must be a Muslim adult, a discerning child who is free of sexual defilement, or an adolescent who is free of menstrual or childbirth bleeding. I’tikaf is not acceptable from an unbeliever, a non-discerning child, a sexually defiled person, a menstruating woman with post-childbirth bleeding.