Musnad Abu Ya'la al-Mawsili 3:168

Surayj ibn Yunus Abu al-Harith narrated to us, Abu Mu'awiyah narrated to us, Abd al-Rahman ibn Ishaq narrated to us, from al-Nu'man ibn Sa'd, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, in Paradise there are chambers whose interiors are seen from their exteriors, and their exteriors are seen from their interiors." A Bedouin said: "For whom are they, O Messenger of Allah?" He said: "For those who spoke good words, fed the food, spread the greeting of peace, and prayed at night while the people were sleeping."