Sahih Muslim
The Book Pertaining to Piety and Softening of Hearts (Kitab Al-Zuhd wa Al-Raqaiq)
Book Number: 042 / Hadith Number: 7087
'A'isha reported: Never could the family of Muhammad (may peace. be upon him) (afford to eat) the bread of wheat for three (successive days) until he ran the course of his life.