ActiveRecord 'where' clause using function

I am trying to apply filters on an ActiveRecord::Relation. I would like to apply a 'where' clause (or the equivalent) to make the following call.

record = Record.all
record.where(record.remaing_units > 5)

I know this would be easy to get coding a fonction and passing it 2 arguments but I would like to know if there is a cleaner way to do it, more 'where' like.