Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.156.
Section : Retiring of the Mu’takif to the Mosque and Setting Up of a Tent.
Ibn Majah recorded from Ibn ‘Umar that the Prophet made i’tikaf during the last ten days of Ramadan. Nafi’ reported: “Ibn ‘Umar showed me the place where the Prophet would perform his i’tikaf.”
He also reported that when the Prophet performed i’tikaf, he would spread out his bed behind the repentance pole (that is, the pole that a companion had tied himself to until Allah accepted his repentance).
Abu Sa’id reported that the Prophet performed i’tikaf under a Turkish tent which had something over its openings.