Incest

What the Bible Says… 

• [Prophet Abraham (pbuh) married his sister]

Abraham replied.. Besides, she really is my sister, the daughter of my father though not my mother; and so she became my wife. (Genesis 20:11,12). 

• [Prophet Lot (pbuh) and his daughters]

… That night they got their father to drink wine and the older daughter went in and lay with him. He was not aware of it when she lay down or when she got up. .. So both of Lot's daughters became pregnant by their father. (Genesis 19:30-36). 

• [Reubun and his father's concubine]

While Israel (Jacob) was living in that region, Reuben want in and slept with his father's concubine Bilhah, and Israel heard of it. (Genesis 35: 22).

• [Judah and his daughter-in-law Tamar]

When Judah saw her (Tamar), he thought she was a prostitute, for she had covered her face.Not realizing that she was his daughter-in-law, he went over to her by the roadside and said, "Come now, let me sleep with you.".. So he gave them to her and slept with her and she became pregnant by him.(Genesis 38:15-18). 



Commentary… 
Incest is a great sin and betrayal of trust by someone supposed to be a protector not an offender. It is religiously, morally and naturally rejected and detested. 
Allah revealed His Books as light and guidance to lead all humans out of darkness and to warn them and guard them against evil. These Books command righteous deeds and forbid shameful deeds and wickedness.
It is true that Allah does mention in His books crimes and sins committed by some people. However, Allah mentions these stories to warn people against committing such sins and crime, and not to encourage people to commit them. When a book mentions very indecent stories of incest or adultery without criticizing or punishing the people who committed them., then the book, in fact, encourages people to do the same. In the Bible:

• Prophet Lot (pbuh) is accused of committing incest with his daughters night after night and there is no criticism. 
• Judah committed incest with his daughter-in-law Tamar and Allah rewarded Judah for this crime with two sons born of incest and one of them was (according to the Bible) a great grandfather of Prophet Jesus (pbuh), although he was born miraculously without a father!
• Reuben committed incest with his father's concubine Bilhah, without any reaction from his father Prophet Jacob (pbuh). 

What is the moral teaching of these immoral stories? Does any upright person want his or her sons and daughters to read them? These fabricated stories have no benefit except spreading immortality and evil on earth and damaging the reputation of Prophets and righteous people. These stories cannot be the Word of Allah and cannot be from the teachings of the Prophets. 



What the Qur'an Says…
Verily, those who like that illegal sexual intercourse should be spread among the believers, will have a painful torment in this world and in the Hereafter and Allah knows and you know not. (Qur'an, 24:19).