Exodus 19.12, 13
Septuagint

prosecete eautoiV tou anabhnai eiV to oroV, kai 
qigein 
ti autou:  paV  o ayamenoV 
tou orouV, 
qanatw teleuthsei.  ouc ayetai autou ceir:  en gar liqoiV 
liqobolhqhsetai
h bolidi katatoxeuqhsetai:  ean te kthnoV ean te anqrwpoV, ou zhsetai

New Testament - Hebrews 12.20

ouk eferon gar to diastellomenon: 
kan qhrion qigh
tou orouV, 
liqobolhqhsetai

 

Septuagint

Take heed to yourselves that ye go not up into the mountain, nor touch any part of it; every one that touches the mountain shall surely die.  A hand shall not touch it, for every one that touches shall be stoned with stones or shot through with a dart, whether beast or whether man, it shall not live

New Testament

for they could not endure that which was enjoined, If even a beast touch the mountain, it shall be stoned

Masoretic Text

Take heed to yourselves, that ye go not up into the mount, or touch the border of it:  whosoever toucheth the mount shall be surely put to death:  no hand shall touch him, but he shall surely be stoned, or shot through; whether it be beast or man, he shall not live

Comments:  The NT, LXX and MT agree.  Clearly, a very loose quotation.

Textus Receptus (and so the Authorized Version) adds h bolidi katatoxeuqhsetai (or thrust through with a dart) immediately after “it shall be stoned” - in agreement with the Septuagint.