When a person wants to do something or say something and someone else beats him to it, is it Sunnah to say “His life will be longer than his” i.e., the life of the one who spoke first will be longer than the life of the one who wanted to say it. Is saying this Sunnah?.
There is no basis in the Sunnah for saying this as far as we know. If the same words or idea cross the minds of two or more people, there is nothing strange about that. If one person says it first, that does not indicate that his life will be long or short.
And Allaah knows best.