Isaiah 49.6
Septuagint

idou dedwka se eiV diaqhkhn genouV, 
eiV fwV eqnwn, tou einai se eiV swthrian ewV escatou thV ghV

New Testament - Acts 13.47

teqeika se 
eiV fwV eqnwn tou einai se eiV swthrian ewV escatou thV ghV

Septuagint

I have given thee for a covenant of a race, for a light of the Gentiles, that thou shouldest be for salvation to the end of the earth

New Testament

I have set thee for a light of the Gentiles, That thou shouldest be for salvation unto the uttermost part of the earth 

Masoretic Text

I will give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth

Comments:  The NT and the LXX agree.  The MT differs.  To be salvation and to be for salvation are different concepts.  The RSV translates this portion as, I will give you as a light to the nations, that my salvation may reach to the ends of the earth.  Even with this reading, the MT differs slightly.