John 8:51
“Verily, verily, I say unto you, If a man keep My saying, he shall never see death.”
Here He speaks not of faith only, but of a pure life. Above He said, “shall have everlasting life,” but here, “shall not see death.” At the same time He hints to them that they could do nothing against Him, for if the man that should keep His saying should not die, much less should He Himself. At least they understood it so, and said to Him,
Source: Homilies on the Gospel of John (New Advent)