As-salam alykom.I am a revert to Isalm, alhamdulilah. My family recently discovered my father was born from zina. We found this out from DNA ethnicity testing. So his last name is not the name of his biological father but rather the man who raised him. Despite having concrete evidence of this he is concealing the evidence from the man who raised him and actively and intentionally spreading false information about family heritage resulting in others believing a false lineage. Since I am aware of all of this information, am I too guilty of taking a false lineage? In this case, is it permissible I change my last name away from people I am not related to?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu`alayhi wa sallam, is His slave and Messenger.

First of all, praise be to Allah, the Almighty, for guiding you to Islam, and we ask Allah to keep us all steadfast on Islam until we meet Him. As for your question, our answer to it is summarized as follows:

First: It is not permissible to accuse your father’s mother of having committed Zina (adultery) without legal evidence. The accusation of Zina is a grave matter and entails legal rulings. Even a non-Muslim is not allowed to be accused of Zina without legal evidence. Even though the accuser is to be punished by Ta’zeer (discretionary punishment), not by Hadd (the corporal punishment determined by the Islamic Law), still it is forbidden to slander her. The scholars stated that slandering a non-Muslim woman is a minor sin. Al-Manawi  said in Fayd al-Qadeer: “[In] the slander of chaste “believing” women, [the word ‘believing’] is a qualification that precludes slandering non-Muslims, as slandering the latter counts as a minor sin.”

The legal evidence on Zina is established by the confession of the one who committed it, or by four witnesses testifying that they have clearly seen the act of fornication. Ibn Rushd, may Allaah have mercy upon him, said in Bidayat Al-Mujtahid: “The scholars unanimously agreed that Zina is proven by confession and testimony.” He also stated: “As for the witnesses' proof of Zina, the scholars unanimously agreed that it is proven by witnesses, and that, unlike other cases, the required number of witnesses is four. Allah, the Almighty, said, {And those who accuse chaste women and then do not produce four witnesses…} [Quran 24:4]. The four witnesses should be just and of upright character who have seen the act clearly (i.e. penetration), and should give the testimony in clear and not in implied words.”

Second: If your father’s mother had been married when your father was born, it will not be correct for his lineage to be denied from her husband just because their DNAs are different. Rather, he is considered the son of her husband and may not be affiliated to the one who committed Zina with her. This is based on the Prophet’s, sallallaahu`alayhi wa sallam, saying: “The child is to be attributed to one on whose bed it is born, and for a fornicator there is stoning.” [Al-Bukhari and Muslim]. According to Al-Bukhari’s narration, “The child is attributed to the owner of the bed.” Here, the owner of the bed is the husband who sleeps with his wife on such bed. Therefore, the child is attributed to him, not the fornicator. Ibn Al-Atheer said in An-Nihayah: “A woman is called a firash (bed) because the husband sleeps with her on his bed. This entails that a child would be attributed to the owner of the bed, whether he is a husband or a master [of the woman], or one who had intercourse with her based on a presumed legal relationship. In all cases, a fornicator has no claim to the child [born out of wedlock].”

Third: Since it is established that it is not permissible to deny the lineage of the newborn from her husband at the time of its birth simply because the DNA is different, the lineage may not be denied except when Li’an (sworn allegation of adultery) is undertaken by that husband [against the wife]. If the husband does not deny the lineage of the child by recourse to Li’an, it shall be considered his child. In which case, you are not allowed to change the lineage. Therefore, you are obliged to keep your lineage as it is, since it is legally valid. It was stated in a Hadith that: “Whoever attributes himself to other than his father, or is related to other than his own master, there is upon him the curse of Allah, the angels, and all the people.” [Muslim and others].

Allah knows best.