(a) Amrah narrates from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to pray in his room, and the wall of the room was low. People saw him (peace and blessings be upon him) standing in prayer, so they too began standing in prayer with the Prophet (peace and blessings be upon him). In the morning they talked about it. The next night the Prophet (peace and blessings be upon him) stood in prayer, and the people prayed with him (peace and blessings be upon him) too. They did this for two or three nights. After that the Messenger of Allah (peace and blessings be upon him) did not come out. In the morning the people mentioned it, and he (peace and blessings be upon him) said: "I feared that the night prayer might be made obligatory upon you."
(b) The hadith of Sayyiduna Zayd bin Thabit (may Allah be pleased with him) indicates that the room was in the mosque.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5239