God calls to the Abode of Peace and He guides whom He wills to a straight path.
(Qur'an, 10:25)

Those who think that they will be successful by causing wickedness, upheaval and oppression, and by killing innocent people are committing a great error. Allah has forbidden all acts of wickedness involving terrorism and violence, condemned those who engage in such acts and said " Allah does not uphold the works of those who cause mischief." in one of His verses. (Qur'an Surah Yunus, 81)

...if someone kills another person - unless it is in retaliation for someone else or for causing corruption in the earth - it is as if he had murdered all mankind. And if anyone gives life to another person, it is as if he had given life to all mankind... (Qur'an Surat al-Ma'ida, 32)

In Sura Ma'ida, verse 32, Allah says that if anyone kills someone unjustly, it is as if he had murdered all mankind. To murder even one person is totally opposed to the moral teaching of the Qur'an.

God commands justice and doing good and giving to relatives. And He forbids indecency and doing wrong and tyranny. He warns you so that hopefully you will pay heed. (Qur'an, 16:90)