Nah, he says "Never!" as he charges towards Vader. It´s hard to make out exactly what he says, but this is from imdb.com (probably taken directly from the script):

Darth Vader : You cannot hide forever, Luke.
Luke : I will not fight you.
Darth Vader : Give yourself to the Dark Side. It is the only way you can save your friends. Yes. Your thoughts betray you. Your feelings for them are strong. Especially for... sister. So, you have a twin sister. Your feelings have now betrayed her, too. Obi-Wan was wise to hide her from me. Now his failure is complete. If you will not turn to the Dark Side... then perhaps she will.
Luke : NEVER!

peace,

Rebelscum