"...If the party liable is mentally deficient, or weak, or unable Himself to dictate, Let his guardian dictate faithfully, and get two witnesses, out of your own men, and if there are not two men, then a man and two women, such as ye choose, for witnesses, so that if one of them errs, the other can remind her. The witnesses should not refuse when they are called on (For evidence)." - Quran 2:282 (read more)

"Narrated 'Abdullah bin 'Umar : The Jew brought to the Prophet a man and a woman from amongst them who have committed (adultery) illegal sexual intercourse. He ordered both of them to be stoned (to death), near the place of offering the funeral prayers beside the mosque." - Sahih Bukhari 7:62:64 (read more)

"The marriage of a Christian man to a Muslim woman is an invalid marriage. Allah says in the Quran, "And give not [Muslim women] in marriage to idolaters until they believe" (al-Baqara 221). Therefore, it is not allowed for a disbeliever to marry a Muslim woman... If he does marry her, the marriage is invalid. The children are the children of fornication. They are to be given to their mother and ascribed to her alone." - Shaikh ibn Baz