Answering the question in point, Dr. Muzammil H. Siddiqi, former President of the Islamic Society of North America, states:
"Marriages between first cousins are allowed in Islam. In surat an-Nisa' (4:22-24), Allah mentioned the women who are forbidden for marriage and then He said, "… Lawful to you are all beyond those mentioned, so that you may seek them with your wealth in honest wedlock…" In surat al-Ahzab (33:50), Allah mentioned to the Prophet that he may marry the daughters of his uncles and aunts from the father's side or the mother's side. It is the consensus of the jurists that this permission was not only for the Prophet, but it is also a permission for other believers. Muslims have practiced marriages between first cousins in all countries since the time of the Prophet.
Such marriages are allowed in many other religions and cultures as well. In United States, most of the states allow marriages between the first cousins. There is nothing wrong in this marriage.
However, it is a good practice to have a blood test before marriage. If one suspects some hereditary disease or any other problem then he/she should seek the advice of a medical expert in this field. The chances of health risk in this marriage are very rare. Most of the marriages have been good and children quite healthy."
Excerpted, with slight modifications from: http://pakistanlink.com/religion.html
Elaborating on this issue, we'd like to cite the fatwa issued by Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author. He states:
"There is no objection whatsoever in the Islamic religion for a man to marry any of his relatives except those forbidden for marriage whom Allah mentioned in surat an-Nisaa' (4: 23) Thus, when Allah mentioned for us the relatives to whom marriage is forbidden, we then come to know that there is no objection for the remainder of the family relations.
Among the most prominent evidence of this fact is that the Prophet (peace and blessings be upon him) married his daughter Fatimah to `Ali (may Allah be pleased with them) and he is the son of her father's uncle, as well as the marriage of the Prophet himself to Zaynab bint Jahsh (may Allah be pleased with her) and she is his aunt's daughter (i.e. his cousin); and there are many other such examples.
However, a different question may be asked, namely: "Is it better or preferable for a Muslim to marry someone he is not related to rather than a relative?"
The answer to this question varies from case to case, and perhaps it may be preferable to marry people who are non-relations, for example if one aspires to form new social ties or bonds, and regards the existence of a marriage relationship with a different family as constructive in widening the circle of social bonds." (Source: www.islam-qa.com)
Elaborating on the issue whether it is preferable not to marry close cousins, we’d like to cite for you the following fatwa:
“Islam permits marriage between first cousins. If we read the Qur'anic verses which enumerate women to whom a Muslim cannot be married, you will find that this list does not include cousins.
The Islamic view is that while marriage between cousins is permissible, it is preferable to choose a marriage partner from outside one's family. We have to distinguish between what is permitted and what is advocated. Some clans restrict marriages to amongst their kin only – a practice far from what is advocated. It is worth stressing here that when marriage of cousins is repeated over several generations, they are bound to have more effects on children.
By permitting such marriages Islam does not encourage them. It advocates the cementing of social relations through marriages between totally unrelated families.
The Prophet (peace and blessings be upon him) once told one of his Companions to choose a wife from a tribe different to his, and then to choose for his son a wife from a third tribe, and to seek for his second son a girl from yet another tribe.
Preferring this course of action, Islam nevertheless permits marriage between cousins because it meets a social need.”
Excerpted, with modifications, from: www.islamicity.com
In conclusion, it is clear that Islam, undoubtedly, permits marrying cousins. As for the issue of preferring to choose a marriage partner from outside one's family, this varies from one case to another. Yet, Islam is generally keen to widen the circle of social bonds. As for the fear of hereditary diseases, it is a good practice to have a blood test before marriage. If one suspects some hereditary disease or any other problem then he/she should seek the advice of a medical expert in this field.
May Allah guide you to the straight path and direct you to that which pleases Him, Ameen.
And another fatwa:
In the name of Allah, Most Compassionate, Most Merciful,
The Messenger of Allah (Allah bless him & give him peace) himself explained the criterion on which a life partner should be chosen.
Sayyiduna Abu Huraira (Allah be pleased with him) reports that the Messenger of Allah (Allah bless him & give him peace) said: "If one, whose Deen and good character pleases you, requests you for marriage, then accept his request, otherwise there will be great trial (fitna) and widespread destruction". (Sunan Tirmizi, 1/207).
In another Hadith, the Messenger of Allah (Allah bless him & give him peace) said: "A woman is married for four reasons, her wealth, lineage, status and Deen. So choose the one who is religious". (Sahih al-Bukhari, 2/762).
Thus, the Messenger of Allah (Allah bless him & give him peace) clearly mentioned that the criterion on which a marriage partner should be selected is a person's Deen and good manners.
Suitability and compatibility (kafa'a) is also one of the important things that need to be considered when choosing a spouse. One of the main ingredients for a prosperous and successful marriage is compatibility. The greater the compatibility and more similar your goals and outlooks, the more likely is the prospect of a successful marriage.
The Messenger of Allah (Allah bless him & give him peace) is reported to have said:
'When you find a suitable partner for a widow (non-married woman, m), then conduct the marriage without any delay' (Sunan Tirmizi, 1/206).
The above is clear in determining that the most important aspect that needs to be considered when choosing a spouse is one's religious inclination and manners. There is no mention of looking for a spouse in the family.
Compatibility is encouraged, but that does not necessarily mean looking for a spouse within the family. Many times, you may have so much in common with somebody from a total different background, whereas no chemistry is found between first cousins.
There are many examples where the Messenger of Allah (Allah bless him & give him peace) and the Companions (Sahaba, Allah be pleased with them all) contracted marriages outside the family. Thus, to place exaggerated emphasis on marriages within the family based purely on pride of ancestry and lineage is something that Islam disapproves of.
And Allah knows best
Muhammad ibn Adam al-Kawthari
Darul Iftaa, Leicester, UK