"Until, when he reached the setting of the sun, he found it set in a spring of murky water: Near it he found a People: We said: “O Zul-qarnain! (thou hast authority,) either to punish them, or to treat them with kindness." - Quran 18:86 (read more)

"Narrated Anas: The climate of Medina did not suit some people, so the Prophet ordered them to follow his shepherd, i.e. his camels, and drink their milk and urine (as a medicine). So they followed the shepherd that is the camels and drank their milk and urine till their bodies became healthy. Then they killed the shepherd and drove away the camels. When the news reached the Prophet he sent some people in their pursuit...." - Sahih Bukhari 1:5:268 (read more)

"Allah says: "There is no compulsion in religion"...But, this verse is abrogated by the verse of "fighting...Therefore, all people of the world should be called to Islam. If anyone of them refuses to do so, or refuses to pay the Jizya they should be fought till they are killed. This is the meaning of compulsion. In the Sahih, the Prophet said: "Allah wonders at those people who will enter Paradise in chains", meaning prisoners brought in chains to the Islamic state, then they embrace Islam..." - Ibn Kathir