I am going to design an SSRS dashboard and I am wondering if it is really mandatory that I should create a cube using SSAS to then be read by SSRS?
I am asking because I can read directly from data base tables or Views.
You do not need a cube, though depending on your requirements, one may be beneficial.
You can use SQL code to extract your data in embedded or shared datasets, or use stored procedures held within your SQL Server database.
The approach you take will depend entirely on your current situation and you will need to research which is the most appropriate yourself, as we will never be able to give you a fully reasoned and justified answer in the Stack Overflow Q&A format.