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Sahl Ibn al-Hasan al-Khurasani who was one of the followers of Ahlul- Bayt in Khurasan (a province in Iran) came to Medina to meet Imam Ja’far al-Sadiq (as). Sahl al-Khurasani said: "O son of the Messenger of Allah! You are of the Imams of Ahlul-Bayt. What prevents you from getting your right (i.e., the rule) while you find more than one hundred thousand Shi’a who are ready to fight for you?”

The Imam (as) asked him to sit down, and then ordered to turn on the oven that was in the house. After the oven became very hot and turned red, the Imam (as) said: "O Khurasani step into the oven and sit in it.”The Khurasani said: "My master, O son of the Messenger of Allah! Do not punish me by fire and make it easy for me.”

At this time, Harun al-Makki (ra) entered the room, and after the greetings exchanged, the Imam (as) told him to put down his shoes and to sit down inside the oven. He did so and the Imam (as) started talking to Sahl about Khurasan as if nothing has happened.

After some time, the Imam (as) said: "O Khurasani stand up and look inside the oven.”Sahl looked into the oven and saw Harun sitting cross-legged inside the fire. Then Imam al-Sadiq (as) asked Harun to come out of oven and he came out healthy with no burn or injury.

At this time, the Imam (as) asked Sahl: "How many individuals do you know in Khurasan like this man?”

Sahl replied: "By Allah, not even one.”The Imam (as) confirmed his saying and said, "We do not rise at this time when we do not even have five helpers (like him). We know better about the proper time.”

(Bihar, v47, p123, Hadith #172; also in Manaqib by Ibn Shahr Ashub)

[I copy and pasted that from A Shi'ite Encyclopedia because I am a little lazy]