Sunan Ibn Majah, Chapter: The Chapters on Ascetism (Zuhd)

"I entered upon the Messenger of Allah (saw) when he was (sitting) on a reed mat. I sat down and (saw that) he was wearing a waist wrap, and there was no other barrier between him and the mat but his waist wrap, and the reed mat had made marks on his side. And I saw a handful of barley, nearly a Sa, and some acacia leaves, in a corner of the room, and a skin hanging up. My eyes flowed with tears, and he said: Why are you weeping, O son of Khattab? I said: O Prophet of Allah, why should I not weep? This mat has made marks on your side, and this is all you have accumulated, I cannot see anything other than what I see (here), while Chosroes and Caesar live among fruits and rivers. You are the Prophet of Allah and His Chosen One, and this is what you have accumulated. He said: O son of Khattab, does it not please you (to know) that (these things) are for us in the Hereafter and for them in this world? He said: Yes."