The first bond of mankind is the bond of husband and wife. When Allah created our original father, Adam, he created them and gave them the opportunity to live in Paradise. But in the instigation of Satan, he sent them to earth to eat fruit of the prohibited tree. Then they started living together on earth and got children. Adam and Eve (A) got a total of eighty pairs (a boy and a girl). At that time, the marriage of the couple with the son of the pair of the pair of the pair of the pair of the pair of the pair of the pair of the pair of the pair of the pair of previous pair were married at the order of Allah at that time. Then, married in the midst of a brother’s sister, only for the sake of need.
With the change in time, there has been a ban on the marriage of people with blood relations in Islam. For a boy who has been banned in Islam for the sake of a boy are: mother, daughter-in-law, sister, phefu, aunt, niece, grandmother, grandmother, daughter of a girl, daughter of daughter, sister-in-law, milk-mother (in case of milking, Drinking), milk sisters, noble daughter, wife of a son born, and two sisters at the same time. (Surah An-Nisa: 23-24).
Apart from these few relations, Islam has not forbidden anyone to marry any other relationship. Our Prophet (peace be upon him) had given the marriage of his favorite daughter Fatima (R) with Hazrat Ali (R), who was the son of the uncle of Prophet (pbuh). The Prophet (pbuh) also married Zainab bint Jas, who was the uncle of the Prophet (pbuh). Therefore, marriage is not banned in Islam except for the mentioned relatives.
But Imam Shafei (Rh) says: “The community of women who do not marry any outside man and men do not marry any outside girl, their children are stupid. (Al-Intaqi Feiadiyilis Salaachatil Ayimmah 1/98). Besides, one of the guidance given by Imam Ghazali (Rh) to choose a bride is that the bride is not a close relative. Because it will reduce their biological desire. (Iyiu Ulumuddin: 2/41). Many Islamic scholars agree that the child is weak when close relatives like -futatto, cousin, cousin, khalatos brothers and sisters get married. That is why it is said that marriage is better with distant people.