"Also (forbidden are) women already married, except those whom your right hands possess. Thus has Allah ordained for you. All others are lawful, provided you seek them from your property, desiring chastity, not fornication. So with those among them whom you have enjoyed, give them their required due, but if you agree mutually after the requirement (has been determined), there is no sin on you. Surely, Allah is Ever All-Knowing, All-Wise." - Quran 4:24 (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)

"The actual example of one of the greatest Companions, `Ali ibn Abi Talib (may Allah be pleased with him) gives credit to this [death sentence for apostasy] also. He himself carried out the punishment on some people who had deified him. He gave them three days respite to repent and go back to their senses. When they proved adamant, he put them to fire." - IslamOnline