Musnad Ahmad 32:1553

Hassan narrated to us, Shayban narrated to us, from Qatadah, from Anas bin Malik, who said: The Prophet of Allah, peace and blessings of Allah be upon him, was invited one day to barley bread and rancid fat. He said: And I heard him one day, repeatedly, saying: "By the One in Whose hand is the soul of Muhammad, the family of Muhammad did not wake up with a *sa'* of grain, nor a *sa'* of dates," even though he had nine wives at that time. And he had pledged a coat of mail of his to a Jew in Medina, from whom he had taken food, and he did not find anything with which to redeem it.