Sayyiduna Hudhayfah (may Allah be pleased with him) said to Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him): (People are) performing i'tikaf between your house and the house of Sayyiduna Abu Musa (may Allah be pleased with him), while I know that the Messenger of Allah (peace and blessings be upon him) said: "There is no i'tikaf except in al-Masjid al-Haram," or he (peace and blessings be upon him) said: "except in the three mosques." Abdullah bin Mas'ud (may Allah be pleased with him) said: Perhaps you forgot and they remembered, or you erred and they were right. (The narrator said:) The doubt is from me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8574