Muhammad ibn Yaqub narrated that, from a number of our companions, from Sahl ibn Ziyad, from Ibn Mahbub, from Umar ibn Yazid, who said: I (narrator) said to Abu Abdillah عليه السلام, peace be upon him: “What do you say regarding seclusion for worship (itikaf) in Baghdad in some of its mosques?” Imam عليه السلام said: “There is no seclusion for worship except in a mosque of congregation in which a just (divinely appointed) Imam has prayed the congregational prayer. And there is no problem with seclusion for worship being observed in the Mosque of Kufa, the Mosque of Madinah, and the Mosque of Mecca.” (and also the Mosque of Basra)