In order to give him a practical answer, the Imam ordered the furnace to be lighted and then instructed Sahl to jump into the flames. Sahl was shocked and said: "O my Master! May God shower you with His grace and favours! Do not place me in the fire. I take back my words and request you to withdraw your instruction".
After a while, Haroun Makki, a sincere companion of the Imam entered and greeted. As soon as the Imam saw him, he told him to take off his slippers and walk into the hot furnace. Without any question, Haroun complied. Imam then turned towards Sahl and began inquiring about Khurasan as if nothing had happened. All this time, Sahl appeared uncomfortable and disturbed worrying about the plight of Haroun in the furnace. Finally the Imam asked him to get up and to look inside the furnace. Sahl witnessed that Haroun was seated comfortably and unharmed in the fiery flames.
Imam asked, "How many such Shia'hs exist in Khurasan?" Sahl said, "By Allah! Not a single Shia'h like Haroun exists in Khurasan". Thereupon, the Imam said, "I shall not stage an uprising when I do not have even five sincere companions. (And do remember) we are very well aware as to when we should stage an uprising". (Safeenatul-Bihar)
Perhaps this incident conveys one of the reasons why our 12th Imam (AJ) has still not come out of his concealment?
Its easy for us to call on him but we must also ask ourselves how many of us are sincere in what we say? How many of us are prepared for his arrival? And how many of us lead a lifestyle, which is in conformity to his teachings?