Musnad Ahmad Hadith 21057

It is narrated from Khabbab (may Allah be pleased with him) that once we presented ourselves in the court of the Prophet (peace be upon him). At that time, the Prophet (peace be upon him) was sitting in the shade of the Ka'bah, reclining on his cloak. We said, "O Messenger of Allah, pray to Allah for us and seek help for us." Upon hearing this, the face of the Prophet (peace be upon him) turned red and he said, "For the people before you, pits were dug as punishment for accepting the religion, and saws were placed on their heads and their heads were split open, but this did not turn them away from their religion. Similarly, iron combs were used to tear the flesh and nerves from behind their bones, but even this pain did not turn them away from their religion. And Allah will surely complete this religion, until a rider will travel from Sana'a to Hadramaut fearing none but Allah, or fearing the attack of a wolf on his sheep. But you people are hasty."