It is narrated from Imam Baqir (AS) who said:

Thirty thousand people gathered to kill our great grandfather, Imam Hussain (AS) in order to get close to God [1]! Because they used to say: Yazid is the Caliph of the Prophet (PBUH)! And Hussain ibn Ali (AS) revolted against him! We must fight Hussain (AS) with our swords. So, the falsehood uses the power of the truth; like parasite that feeds on the body and the blood of the human being; when someone wants to follow his inordinate desires, what does he do?

From the power of the truth, brings in a heresy wrapped in the clothes of the religion, because he knows, the power is from the religion. Meaning, he uses the power of the Quran, the Prophet (PBUH), and Imam (AS), and labels something which is not real, as the truth. Therefore, if the falsehood is separated from the truth and is not mixed with the truth, the seekers of the truth will not be deviated. And if the truth is separated from the cover of the falsehood and is freed, the tongue of malicious one will be cut [2].

[1] Maqtalul Hussain (AS), Moqarram, Page 6.

[2] Nahjul Balaghah, Sermon 50.

Source:en.shafaqna.com