Quran chapter 6 surah 6. 

Do not kill a person because God has forbidden killing (Quran 6:151).


Why is the Quran in Arabic.

The Quran is in Arabic so that Arabs could not say in the hereafter that they did not know about the Day of Resurrection and Judgement about which the Jews were warned in the Hebrew Torah Taurat and the Christians were warned in the Greek Gospel Injil (Quran 6:155, Quran 6:156, Quran 6:157).