"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 'Aisha: that the Prophet married her when she was six years old and he consummated his marriage when she was nine years old, and then she remained with him for nine years (i.e., till his death)." - Sahih Bukhari 7:62:64 (read more)

"...it is not permissible to marry her [an atheist], as she is still a Kafir (non-Muslim) and has not yet embraced Islam wholeheartedly without any doubt. Allah says: "And do not marry Al-Mushrikât (idolatresses, etc.) till they believe (worship Allâh Alone). And indeed a slave woman who believes is better than a (free) Mushrikah (idolatress, etc.), even though she pleases you."(Al-Baqarah 2:221). Being convinced by Islam and wishing to embrace it is not an excuse for you to get married with her..." - Dr. Abdullah Al-faqih