Imam Sadiq (peace be upon him): Zurarah said: Imam Sadiq (peace be upon him) was asked about how the progeny of Adam (peace be upon him) and his children began, because we have people who say: "Allah the Exalted revealed to Adam (peace be upon him) that he should marry his daughters to his sons, and therefore the root of all this creation is from [the marriage of] brothers and sisters." Imam Sadiq (peace be upon him) said: "Allah is far exalted above what they say. Those who say this believe that Allah the Exalted created the elite of His creation, and His beloved ones, and the prophets and messengers, and the believing men and women, and the Muslim men and women, from something unlawful, and that He did not have the power to create them from something lawful — whereas Allah has taken from them a pure, clean, wholesome and lawful covenant. By Allah, I have been informed that one of the animals did not recognise its sister, and when it mated with her and ejaculated, she seemed familiar to it; and when it realised that she was its sister, it drew out its private part and gripped it with its teeth and pulled at it until it severed it, then fell to the ground and died. And another animal [I know of] which, without recognising its mother, did the same with her, and it too did the same thing to itself [and killed itself]. So how can a human being, with his humanity and his knowledge and understanding, do such a thing? A generation of these people whom you see refused to take knowledge from the Ahl al-Bayt of their prophets, and took it from where they were not commanded to take it. So they became as you see them — drowned in misguidance and ignorance regarding matters of the past, not knowing how things were from the very beginning, when Allah created everything." Then he said: "Woe to them! How can they differ over what the jurists of Hijaz and the jurists of Iraq are in agreement upon? Allah the Exalted commanded the Pen, and the Pen wrote — two thousand years before the creation of Adam (peace be upon him) — everything that has been and everything that will be until the Day of Resurrection; and in all the heavenly books that Allah has sent down, the marriage of brothers with sisters is forbidden along with the other prohibitions. And of these heavenly books, we see in this world these four famous books: the Tawrat, the Injil, the Zabur and the Qur'an, which Allah, the Glorified, sent down from the Preserved Tablet upon His messengers. Among them: the Tawrat upon Musa (peace be upon him), the Zabur upon Dawud (peace be upon him), the Injil upon Isa (peace be upon him), and the Qur'an upon Muhammad (peace be upon him and his family) — and in none of these heavenly books is there anything permitting the marriage of a brother to a sister. The truth is that whoever says such things, or the like of them, is in reality seeking to strengthen and reinforce the arguments of the Magians. Where are they going? May Allah destroy them!" Then he began to speak about how the progeny of Adam (peace be upon him) and his children came into being. He said: "Hawwa gave birth seventy times, and in each birth she bore for Adam (peace be upon him) a daughter and a son — until Habil (peace be upon him) was killed. When Qabil killed Habil (peace be upon him), Adam (peace be upon him) grieved greatly for him and mourned to such an extent that he no longer had any desire to be intimate with women, and for this reason he was unable, for five hundred years, to approach Hawwa (peace be upon her). Then his sorrow and grief and anguish were lifted from him, and he approached Hawwa. Then Allah granted Adam (peace be upon him) Shith (peace be upon him) alone, and the name Shith (peace be upon him) means Hibatullah — that is, the gift of Allah — and he was the first successor (wasi) from among the descendants of Adam upon the earth. After Shith (peace be upon him), Adam (peace be upon him) had another son named Yafith, who was also born alone. When these two grew up, and Allah willed to bring the human race to what you see now, and to preserve [the prohibition of] the marriage of brothers with sisters which He had forbidden and had written in the Preserved Tablet, one Thursday afternoon He sent down a houri from Paradise named Nazlah, and commanded Adam (peace be upon him) to marry her to Shith (peace be upon him); and Adam (peace be upon him) did so. On the following day, in the afternoon, He sent down another houri from Paradise named Manzilah, and commanded Adam (peace be upon him) to marry her to Yafith. Adam (peace be upon him) did so. Thus Shith (peace be upon him) had a son, and Yafith had a daughter. And when they grew up, Allah commanded Adam (peace be upon him) to marry the daughter of Yafith to the son of Shith (peace be upon him). Adam (peace be upon him) did so, and it was in this way that from these two chosen lines the prophets and messengers were born. Refuge with Allah from what these people say about the marriage of brothers and sisters!"