There are some ahaadeeth that condemn the illegitimate child, but most of these ahaadeeth are da’eef (weak) and are not saheeh (sound). It was narrated by Abu Dawood in his Sunan (4/39) and by Ahmad in al-Musnad (2/311) from Abu Hurayrah (may Allaah be pleased with him) that the Prophets (peace and blessings of Allaah be upon him) said: “The illegitimate child is the most evil of the three” meaning more evil than his parents. Among the scholars who classed this as hasan were Ibn al-Qayyim in al-Manaar al-Muneef (133) and al-Albaani in al-Silsilat al-Saheehah (672).
The scholars interpreted this hadeeth in a number of ways, the most famous of which was that suggested by Sufyaan al-Thawri, who said: it means he is the most evil of the three if he does the same action as his parents did (i.e., zina or adultery).
This was narrated from ‘Aa’ishah, who said that the Prophet (peace and blessings of Allaah be upon him) said: “He is the most evil of the three if he does the same action as his parents did – meaning the illegitimate child.” Although its isnaad is da’eef, it was interpreted in this manner by the salaf, as stated above.
This interpretation is supported by the report narrated by al-Haakim (4/100) – with an isnaad of which al-Albaani said, “It may be regarded as hasan” – from ‘Aa’ishah (may Allaah be pleased with her), that the Prophet (peace and blessings of Allaah be upon him) said: “The illegitimate child does not bear any part of his parents’ burden of sin. ‘and no bearer of burdens shall bear the burden of another’ [al-An’aam 6:164 – interpretation of the meaning].” (al-Silsilat al-Saheehah, 2186)
Some scholars said that this hadeeth is to be interpreted as meaning that there is some evil in most illegitimate children because they are created from an evil nutfah (sperm drop), and usually nothing good is created from an evil nutfah. If a good soul comes out of this nutfah then it will enter Paradise. This hadeeth is to be taken as a general rule to which there may be exceptions. (See al-Manaar al-Muneef, 133).
Hence Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said: “If an illegitimate child believes and does righteous deeds, he will enter Paradise, otherwise he will be punished for his deeds just like anyone else. The punishment is for the deeds, not for the lineage. Rather the illegitimate child is condemned because he is expected to do evil deeds, as often happens. By the same token, good lineages are regarded as praiseworthy because such people are expected to do good deeds. But when a person does a deed, then the reward or punishment is based on that, and the most noble of people before Allaah are those who are most pious. (al-Fataawa al-Kubra, 5/83).
It says in Fataawa al-Lajnah al-Daa’imah: “If an illegitimate child dies in Islam (as a Muslim), he will enter Paradise, and his being illegitimate does not have any effect on that, because that was not due to his own actions, rather it was the action of someone else. Allaah says (interpretation of the meaning):
‘and no bearer of burdens shall bear the burden of another’
And Allaah says (interpretation of the meaning):
‘Every person is a pledge for that which he has earned’
And there are other similar verses.
With regard to the words narrated from the Prophet (peace and blessings of Allaah be upon him), ‘No illegitimate child will enter Paradise,’ this hadeeth is not saheeh. It was mentioned by al-Haafiz Ibn Jawzi in al-Mawdoo’aat, but it is one of the ahaadeeth that were fabricated against the Prophet (peace and blessings of Allaah be upon him). And Allaah is the Source of strength.”
With regard to the ruling on marrying one who is illegitimate, none of the reputable fuqaha’ have stated that this is haraam. However there was some difference of opinion among the Hanbalis as to whether such a person is compatible with a woman of good lineage. Some of them said that he is compatible with her, and othesr did not agree with that because that will be a source of shame for the woman, because he will be her guardian, and that would also affect her child. (See al-Mughni, 7/28).
(al-Mawsoo’ah al-Fiqhiyyah, 34/282).
Shaykh Ibn Baaz (may Allaah have mercy on him) was asked about a man who married his daughter to a person who was apparently illegitimate – what was the ruling on that? He answered as follows:
“If he is Muslim, then the marriage is sound, because the sin of his mother and the one who committed zina with her does not rest on him. Allaah says ‘and no bearer of burdens shall bear the burden of another’ [al-An’aam 6:164 – interpretation of the meaning]. And there is no shame on him because of their action, if he adheres steadfastly to the religion of Allaah and develops good characteristics, because Allaah says
‘O mankind! We have created you from a male and a female, and made you into nations and tribes, that you may know one another. Verily, the most honourable of you with Allaah is that (believer) who has At-Taqwa [i.e. he is one of the Muttaqoon (the pious)]. Verily, Allaah is All-Knowing, All-Aware’
And the Prophet (peace and blessings of Allaah be upon him) said, when he was asked who is the most noble of people, ‘Those who are most pious.’ And he (peace and blessings of Allaah be upon him) said: ‘If a person’s actions make him less worthy than others, his lineage will not make him more worthy.’”
From Fataawa Islamiyyah, 3/166.
And Allaah knows best.