Imam Malik (may Allah have mercy on him) narrates from a trustworthy man that after the death of the Prophet (peace and blessings be upon him), people used to enter the chambers of his wives (may Allah be pleased with them) and pray the Friday prayer there, because the mosque had become cramped; they would make room for themselves in them. The chambers of the wives of the Prophet (peace and blessings be upon him) were not part of the mosque, but their doors opened onto the mosque.
Note: Imam Malik (may Allah have mercy on him) says: Whoever prays in the courtyards and the like adjoining the mosque, that will suffice him, and people did not find fault with it. Imam Malik (may Allah have mercy on him) says: If a house is closed and entering it without permission is not allowed, then it is not permissible to pray the Friday prayer with the imam in it, even if that house is close to the mosque, because it is not part of the mosque.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5250