All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Islamic Sharia has given utmost attention and care to the issue of parentage. This is reflected in the fact that preserving parentage is one of the higher objectives of Sharia. This is in addition to enacting provisions related to this issue in terms of legislating marriage, proving paternity, prohibiting Zina (Adultery/fornication) and the like.
Using DNA to prove paternity is a new issue and the ruling of Sharia on this can be derived from the views of the jurists about the methods of proving paternity by analogy to Qiafa (i.e. skill in recognizing the lineage of a person through Physiognomy and through examining the body parts of an infant) adopted by the jurists. In addition, proving paternity through the DNA outweighs Qiafa because the former rests on clearly established scientific bases.
At its sixteenth meeting (21-26/10/1422 AH, corresponding to 5-10/1/2002 AD), the Islamic Fiqh Academy of the Muslim World League stated: "The DNA tests are almost definitive in proving or disproving paternity and tracing back the samples (blood, semen, or saliva) present at the scene to the adulterer. DNA tests are far more accurate than Qiafa."
It goes without saying that proving paternity through the DNA doesn`t outweigh powerful methods in this regard, such as the marriage contract. Thus, it isn`t permissible to prove the paternity of someone whose paternity is already established and was born out a valid marriage. Al-Shirbini said: "There is no need to establish paternity for someone whose paternity is already established." {Moghni Al-Mohtaaj, V.3:304}.
As for proving paternity of an illegitimate child, this isn`t stated in the texts of Sharia according to scholarly consensus, even if the DNA tests have proven paternity to the adulterer, because adultery doesn`t fit as ground for proving parentage. The evidence on this is that the Messenger of Allah said: "The child is for the bed and stoning is for the adulterer." {Agreed upon}. The bed means that the woman conceives out of valid marriage and that her child is the son/daughter of her husband.
However, the child born out of adultery must be attributed to his mother only, so he carries her name and enjoys the rights due to him based on that, such as inheritance, custody, prohibition to marry his mother`s mahrams, and the like.
In conclusion, proving or disproving paternity through the DNA shouldn`t be given precedence over the rules of Sharia, in this regard, nor other powerful means. However, it is permissible to resort to the DNA testing to settle disputes regarding children of unknown parentage, suspecting the identity of the babies born in the hospital, and lost children. However, it isn`t permissible to prove paternity of someone whose paternity is already established. And Allah the Almighty knows best.