In the Qur'an

Here's the root cause of honor killings in Islam, straight from the Qur'an.

FROM CALGARYHERALD.COM:

In the Qur'an

By Steve Harris, Calgary Herald June 17, 2010
Re: "Father, son, admit strangling teen in 'honour' killing," 
June 16.

The reason honour killings occur in Islam is that the practice is mandated in the Qur'an. Verses 18:65-18:81 tell of Moses meeting a man to whom God had given special knowledge. Moses accompanied the man to learn what God had taught him, and when they encountered a youth, the man killed him for no apparent reason. When Moses objected, the man explained that the youth was the son of righteous people and was about to grieve them by entering into insolence and religious infidelity, so he killed him in the hope God would give the couple a better son. According to the Qur'an, Moses clearly accepted this explanation, as he made no further objection. To pre-emptively answer the predictable, "You took this out of context" argument, this story is presented in its entirety without preamble or followup, and is not referred to anywhere else in the Qur'an. Nor can the translation be questioned as the three most trusted translators (Yusuf Ali, Pickthal, and Shakir) tell essentially the same story with different wording.