I've been trying to remember a story in which robots (or more likely people) in far future try to build a time machine. In the end they seem to send an assassin to kill Isaac Asimov so that he couldn't invent the Three Laws of Robotics.
I'm pretty sure that the very last sentence of the story was something like 'Isaac Asimov must die!' but strangely I couldn't find anything googling variations of that sentence.
Does anyone remember a story like that?