Translation of the letter:
Mansoor Hashemi Khorasani intended to write something for people and invite them to Allah and His Caliph, the Mahdi, at the beginning of his invitation. Then he was told: “They do not read the writings of someone they do not know, and there are already too many writings among them!” Therefore, after praising Allah and sending blessings upon His Prophet, he wrote:
As for what follows… O people of understanding! O my Muslim brothers and sisters! I have a word with you. Will you listen to it and set your hearts on it? Or will you block your ears and go on your way? By Allah, if a person’s enemy writes him a letter, he reads it carefully to know what the enemy has written to him. Yet I am a compassionate friend and well-wishing brother to you, and I am more deserving that you know what I have written to you. If you do not know me, I know you, and if you do not like me, I like you. Thus, listen to my word, and do not ask who I am, for a person is known by his word, and the wise person looks at the word and does not look at its speaker. How much truth a child speaks, and how many lies elders tell! Truth is truth, even if spoken by a child, and a lie is a lie, even if told by elders. Therefore, if you know a word, not knowing its speaker will not harm you, and if you do not know a word, knowing its speaker will not benefit you. Then, listen to my word to know who I am, for a person is hidden beneath his tongue and is not known until he speaks. You were not given ears except to hear, and you were not given eyes except to see, and you were not given reason except to know which of the things you hear and see are true and which are false. Therefore, listen to my word with your ears; then think about it with your reason to accept it if true and reject it if false. May Allah grant you success, for Satan wants you not to listen so that you may not know, and not to know so that you may suffer loss, and is loss but the result of ignorance?
I know that those who were before me spoke too much to you and annoyed you, for most of their speech was lies, and they spoke of matters they had no knowledge of. And a group of them does not want you except for themselves and does not speak to you except for deception. They call you to a truth that they themselves do not know, and they desire good for you that they themselves have no share in. They are the ones who have taken religion as a support for power and the Hereafter as an instrument for the world. Otherwise, they have neither truly known the religion nor sincerely desired the Hereafter. However, I speak to you without any hope for power or greed for the world. I am but a man among you. I am considered weak on the Earth just as you are, and I do not seek to be superior to you or to spread corruption on the Earth. I want nothing but to enjoin what is right and forbid what is wrong so that Allah may make whoever He wills hear and make whoever He wills deaf. And what do you know?! Perhaps He will change things and reveal things, for He has power over all things and full knowledge of everything.
Then, he wrote what he intended.