Ibrahim reports that Sayyiduna Hudhayfah (may Allah be pleased with him) came to Sayyiduna Abdullah (may Allah be pleased with him) and said: Shall I not make you wonder at people sitting in i'tikaf between your house and the house of al-Ash'ari (Abu Musa)? Sayyiduna Abdullah (may Allah be pleased with him) said: "Perhaps they are right and you are mistaken." Sayyiduna Hudhayfah (may Allah be pleased with him) said: "I do not care whether I observe i'tikaf there or in this market of yours. I'tikaf is only in these three mosques: the Sacred Mosque, the Mosque of Madinah and al-Aqsa Mosque." And the people who had observed i'tikaf, whom Sayyiduna Hudhayfah (may Allah be pleased with him) criticised, were (secluded) in the great mosque of Kufah.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9477