Answered by Ustadh Tabraze Azam
Question: Assalam alaykum
I am an illegitimate child. Is my half sister mahram to me?
Answer: Assalamu alaikum wa rahmatullah,
Yes, if the lady in question has the same mother as you, she is from your unmarriageable kin (mahram) because she is your half-sister. However, if there is some kind of unwarranted attention which she may get from a half-brother by unveiling in his presence, she should carefully consider the wisdom in doing so.
As part of a longer verse, Allah Most High says, “Also forbidden to you for marriage are your mothers, your daughters, your sisters…” [4:23]
Generally, the basis is that children born out of wedlock are not ascribed to their biological fathers. This is because the establishment of paternal lineage (ithbat al-nasab) is a legal ruling which has specific requirements that don’t return to biological factors. Thus, and even if the father is known, you would not be deemed his son, you would not inherit from him, nor would his children be impermissible for you to marry.
Of course, if the father unconditionally claimed the child in a court setting, lineage would be established and the normal duties of paternity would apply; and with respect to you, his daughters would be impermissible for you to marry, so they need not cover in your presence.
Please note that this is an explanation of the law and limits of the discussion in question, and it has no bearing on the propriety of any such potential marriage.
[Kasani, Bada‘i al-Sana’i; Halabi, Multaqa al-Abhur; Abyani, Sharh al-Ahkam al-Shar‘iyya fi al-Ahwal al-Shakhsiyya (2.875)]
Please also see: Who is Mahram and: Are Step Siblings Mahram? and: Is My Half-Brother From My Unmarriageable Kin (Mahram)?
And Allah Most High alone knows best.
[Ustadh] Tabraze Azam
Checked and Approved by Shaykh Faraz Rabbani
Ustadh Tabraze Azam holds a BSc in Computer Science from the University of Leicester, where he also served as the President of the Islamic Society. He memorised the entire Qur’an in his hometown of Ipswich at the tender age of sixteen, and has since studied the Islamic Sciences in traditional settings in the UK, Jordan and Turkey. He is currently pursuing advanced studies in Jordan, where he is presently based with his family.