"And if you fear that you cannot act equitably towards orphans, then marry such women as seem good to you, two and three and four; but if you fear that you will not do justice (between them), then (marry) only one or what your right hands possess; this is more proper, that you may not deviate from the right course." - Quran 4:3 (read more)

"Narrated Qatada: Anas bin Malik said, "The Prophet used to visit all his wives in a round, during the day and night and they were eleven in number." I asked Anas, "Had the Prophet the strength for it?" Anas replied, "We used to say that the Prophet was given the strength of thirty (men)." And Sa'id said on the authority of Qatada that Anas had told him about nine wives only (not eleven)." - Sahih Bukhari 1:5:268 (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