You cannot say this because url_for only takes one parameter:

url_for(@deal, :tab => 'general') # won't work

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

Just use polymorphic_url instead:

polymorphic_url(@deal, :tab => 'general')

url_for with added params