"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 bin Malik: While we were sitting with the Prophet in the mosque, a man came riding on a camel. He made his camel kneel down in the mosque, tied its foreleg and then said: "Who amongst you is Muhammad?" At that time the Prophet was sitting amongst us (his companions) leaning on his arm. We replied, "This white man reclining on his arm." They then addressed him" - Sahih Bukhari 1:3:63 (read more)

"Islam says that these three groups [Jews, Christians, and Magians] may be given the choice: they may enter Islam or they may pay the jizyah and feel themselves subdued. Some of the scholars are of the view that others may also be given the choice between Islam and jizyah, but the most correct view is that no others should be given this choice, rather these three groups are the only ones who may be given the choice, because the Prophet (peace and blessings of Allaah be upon him) fought the kuffaar in the Arabian Peninsula and he only accepted their becoming Muslim." - Islam Q&A