صحيح البخاري

Narrated Khabbab bin Al-Art:

We complained to Allah's Messenger (about our state) while he was leaning against his sheet cloak in the shade of the Ka`ba. We said, "Will you ask Allah to help us? Will you invoke Allah for us?" He said, "Among those who were before you a (believer) used to be seized and, a pit used to be dug for him and then he used to be placed in it. Then a saw used to be brought and put on his head which would be split into two halves. His flesh might be combed with iron combs and removed from his bones, yet, all that did not cause him to revert from his religion. By Allah! This religion (Islam) will be completed (and triumph) till a rider (traveler) goes from San`a' (the capital of Yemen) to Hadramout fearing nobody except Allah and the wolf lest it should trouble his sheep, but you are impatient." (See Hadith No. 191, Vol. 5)