Psalm 40:7
6 Receiving sacrifices and offerings are not your primary concern. Ears you hollowed out for me.18 You do not ask for burnt sacrifices and sin offerings. 7 Then I say, “Look, I come! What is written in the scroll pertains to me. 8 I want to do what pleases you, my God. Your law dominates my thoughts.”
LXX Psalm 39:7
6 Sacrifices did not please you, but you prepared a body for me. Burnt and sin offerings were not your desire. 7 I understood my calling, as it is written of me. 8 My desire is to fulfill your will, O God, with your law deep within my heart.
Hebrews 10:5
5 So when he came into the world, he said, “Sacrifice and offering you did not desire, but a body you prepared for me. 6 Whole burnt offerings and sin-offerings you took no delight in. 7 Then I said, ‘Here I am: I have come—it is written of me in the scroll of the book—to do your will, O God.’”
Notes and References
"... The interface between textual and exegetical issues is nowhere more evident than in the Epistle to the Hebrews. Of particular interest is 10:5-7, in which the author quotes Psalm 40:6-8a (LXX 39:7-9). As is well known, the quotation differs from the Hebrew in one important respect. In the Masoretic Text, the second clause of verse 7 reads ('ears you have dug for me'), usually interpreted to mean, 'you have opened my ears,' that is, 'you have properly instructed me' (in contrast to the first clause: 'Sacrifice and offering you did not desire'). In Hebrews 10:6, however, we read ('but you prepared a body for me'), which is the reading found in virtually the whole LXX tradition ... Since throughout the Epistle to the Hebrews the author depends on the LXX and appears not to have made use of the Hebrew text, it would follow that h e seized on the LXX s defensible paraphrase to present a messianic Interpretation of the Psalm ... In the light of these considerations, we have good reason to believe that the author of Hebrews had before him a Greek text of Psalms with the reading and that therefore he is the one responsible for changing this word ..."
Jobes, Karen H., and Moisés Silva Invitation to the Septuagint (pp. 195-197) Baker Academic, 2000