Darood e Mahi

one day, while the Prophet (P.B.U.H) was sitting in the mosque of Madina, a villager came. He had a pot in his hand covered with a piece of cloth which he put down before the Prophet Allah (P.B.U.H) I am trying to cook this fish for last three days but fire seems to be totally ineffective over it. t is not cooked nor it recevies the effect of fire. Now I have brought it to You, You better know it.
The Prophet (P.B.U.H) asked the fish about this problem. It started speaking by the order of Allah and said Once I was standing in the water where a man was reciting this Darood Sharif, I received his voice in my ears. I myself did nothing. The Prophet (P.B.U.H) said tell me what was that. The fish recited that Darood Sharif. The Prophet said O Ali, write down this Darood Sharif and teach it to people, the fire of hell will become Haram (Ineffective) over those who recite it, Insha Allah.