Sahih Muslim
The Book Pertaining to Piety and Softening of Hearts (Kitab Al-Zuhd wa Al-Raqaiq)
Book Number: 042 / Hadith Number: 7094
'A'isha reported this hadith through other chains of transmitters also (and the words are) that Allah's Messenger (may peace be upon him) died (in a state) when the people could afford to eat only the dates and water.