Abu Dawud Book 33, Hadith Number 4395.

Narated By AbuDharr : The Apostle of Allah (PBUH) said to me: O AbuDharr: I replied: At your service and at your pleasure, Apostle of Allah! He said: how will you do when death smites people, and a house, meaning a grave, will cost as much as a slave. I said: Allah and His Apostle know best, or he said: What Allah and His Apostle choose for me. He said: Show endurance, or he said: You may show endurance.