Genesis 21.10
Septuagint

kai eipe tw Abraam, 
ekbale thn paidiskhn tauthn, 
kai ton uion authV:  ou gar mh klhronomhsei o uioV thV paidiskhV tauthV meta tou uiou mou Isaak 

New Testament - Galatians 4.30

alla ti legei h grafh;
ekbale thn paidiskhn 
kai ton uion authV:  ou gar mh klhronomhsei o uioV thV paidiskhV meta tou uiou thV eleuqeraV

Septuagint

then she said to Abraam, Cast out this bondwoman and her son, for the son of this bondswoman shall not inherit with my son Isaac

New Testament

Howbeit what saith the scripture?  Cast out the handmaid and her son:  for the son of the handmaid shall not inherit with the son of the freewoman 

Masoretic Text

Wherefore she said unto Abraham, Cast out this handmaid and her son:  for the son of this handmaid shall not be heir with my son, even with Isaac

Comments:  The NT, LXX and MT agree.