Sayyiduna Khabbab (may Allah be pleased with him) narrated: We came to the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was lying with his head resting on his cloak in the shade of the Ka'bah, and we said: O Messenger of Allah! Will you not pray to Allah? Will you not seek help? The narrator said: He (peace and blessings be upon him) sat up, his face red with anger, and then he said: "Among those before you, a pit would be dug for one of them, then he would be placed in it, then a saw would be placed on his head, then he would be combed with iron combs down to what lies beneath his bone, yet that would not turn him away from his religion; but you are being hasty. By Allah! This religion will certainly be completed, until a rider will travel from San'a to Hadramawt fearing none but Allah, and the wolf for his sheep."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3626