Some people offer condolences by saying, “May the rest of his life be added to your life”

This is wrong. What can be left of a person’s life when Allaah says (interpretation of the meaning):

“when their term comes, neither can they delay it nor can they advance it an hour (or a moment)” [al-A’raaf 7:34].

The deceased has died at the time when his lifespan was completed; his death did not come too early or too late, so how can there be anything left of his life?

Moreover, this goes against the Sunnah. The Sunnah in offering condolences is to say “To Allaah belongs what He takes and to Allaah belongs what He gives” or “May Allaah make your reward great” or “May Allaah console you” or “May Allaah forgive your deceased loved one” and so on.