"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)

"Getting married at an early age is something that is confirmed by the book of Allah, the Sunnah of his Prophet (Sallallahu Alaihi wa Sallam), the consensus of the scholars and the actions of the companions, and the Muslims who came after them... There are many Ahadith which confirm that marriage at an early age was widespread among the companions and no one denied its permissibility. Getting married at an early age was not peculiar to the Prophet (Sallallahu Alaihi wa Sallam) as some people think, but it was general for him and for his Ummah." - Islamweb