It should be clear that though Islam encourages raising orphans and greatly rewards those who shelter them, it stipulates that a child should be named after his biological father.
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “Allah says, “He has not made your adopted sons (truly) your sons: these are but (figures of) speech uttered by your mouths — whereas Allah speaks the (absolute) truth: and it is He alone who can show you the right path.” (Al-Ahzab: 4)
Based on the above teachings, no one is allowed to give an adopted child their own name. If this way done in the past prior to embracing Islam, you should change this name. Allah says: “Call them by their (real) fathers; this is more equitable in the sight of Allah; and if you know not who their fathers were, (call them) your brethren in faith and your friends.” (Al-Ahzab: 5)
If a person’s parentage is unknown, then he or she must be named the ‘son or daughter of `Abdullah (servant of Allah)’ or the ‘son or daughter of Amat Allah (maidservant of Allah).’ For example, if your adopted son’s name is ‘John,’ then you should change his name to ‘John, the son of `Abdullah.’ Similarly, if an adopted girl’s name is ‘Mary,’ you should call her ‘Mary, daughter of `Abdullah or Amat Allah.’
In light of the above, it is advisable to change the name of your adopted son.
If, however, you feel strongly that such a change may cause undue emotional trauma for the child, as he will not be able to deal with it at this time, then you may postpone this change of name until he attains the age of maturity when he should be better able to absorb the shock.”