article -view.html.erb

En el article block pones una de estas 

<%= link_to article.user.name, user_path(article.user_id) %>
or 
<%= link_to article.user.name, user_path(article.user.id) %>

routes.rb

  devise_for :users
  resources :users, only: [:show, :index]

users_controller.rb

class UsersController < ApplicationController]
 before_action :set_user, only:[:show]

def show	
end

private
	def set_user
	  	@user = User.find_by(username: params[:id])
	end
end