Musnad Ahmad 1015:13

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Yahya ibn Abi Kathir, from Ibn Ma'aniq or Abu Ma'aniq, from Abu Malik al-Ash'ari, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, in Paradise there is a chamber whose exterior can be seen from its interior, and its interior can be seen from its exterior. Allah has prepared it for those who provide food, speak softly, observe continuous fasting, and pray while the people are asleep."