Abu Wa'il reports that Sayyiduna Hudhayfah (may Allah be pleased with him) said to Sayyiduna Abdullah (may Allah be pleased with him): Some people are sitting in i'tikaf between your house and the house of Abu Musa; will you not forbid them? Sayyiduna Abdullah (may Allah be pleased with him) said to him: "Perhaps they are right and you are mistaken, and they have remembered and you have forgotten." Sayyiduna Hudhayfah (may Allah be pleased with him) said: "There is no i'tikaf except in these three mosques: the Mosque of Madinah, the Mosque of Makkah and the mosque of Bayt al-Maqdis (Iliya)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9478