In a book being published serially, Sayyid Imam points out the lies and double-dealing of Ayman Al Zawhari, and challenges him to a cursing before God. See here at Jihadica, partial list below:
Zawahiri repeatedly says I wrote the Document [the Tarshid] under the supervision of the U.S. and the Jews. He is a liar and I call him to a mubahala. I swear to God that I wrote the Document to help Islam and if Zawahiri has lied about this, may God curse him. What Zawahiri says about the Document he also said about Bin Laden. Zawahiri accused UBL of being an agent of Saudi intelligence working among the Islamic movements when UBL didn’t support them with money in 1995. Zawahiri thinks everyone is a traitor like him. Zawahiri accused me of being an agent of Sudanese intelligence. I swear that I heard Zawahiri say to me in Sudan at the end of 1993 that he had to carry out 10 operations for the Sudanese in Egypt and that he received $100,000 from them to that end. If he denies it, I call him to a second mubahala: I swear Zawahiri said this and if he denies it, may God send his curse down upon him. He began working for the Sudanese a year after I cut off my ties with Islamic Jihad. He paid the Islamic Jihad group in Egypt to carry out operations there. I sat with them and warned them that it was futile and not required by Islamic law, but Zawahiri persisted. He and his brother swore they would go fight in Egypt until they died, but they did not; they let others die there instead.
For those not knowing who this person is, he wrote the book on Jihad originally used to train Al Qaeda, and is one of Ayman Al Zawahiri’s oldest associates.
[ Editor: note that underlying this is not just fear of Allah, and it’s not just personal. A mubahala involves Zawahiri’s family as well, and who is to say how Allah’s will in the curse would be wrought? See this section from Wiki:
Muhammad called them to Mubahala(Cursing), where each party should ask God to destroy the lying party and their families. Muhammad, to prove to them that he is a prophet, brought his daughter Fatimah and his surviving grandchildren, Hasan and Hussein, and Ali ibn Abi Talib and came back to the Christians and said this is my family (Ahl al-Bayt) and covered himself and his family with a cloak