Musnad Abu Ya'la al-Mawsili 152:224

Abu Khaythama narrated to us, Yazid ibn Harun narrated to us, he said: al-Mas'udi narrated to us, from 'Amr ibn Murrah, from Ibrahim, from 'Alqama, from 'Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) slept on a mat which had left a mark on his side. We said: "O Messenger of Allah, would you not have informed us so that we could have spread something softer than it beneath you?" He said: "What do I have to do with the world? My likeness and the likeness of the world is only like a rider who traveled on a hot summer day, then rested under a tree, then departed and left it."