Money Transactions in a Family (General Income Tax Query)

This query is regarding my friend :-

My friend father given money around 3 Lakh to his son approx 2 years ago for purchasing of new car. The son bought a new car on loan approx. 10 lakhs ( 3 Lakh down payment approx + 7 Lakh loan approx.). Now after around 2 years son sold the same car approx. 6.5 Lakhs. Please note all Loan installments have been finished. Now son wants to transfer money around 6.5 Lakhs to his father saving bank account.

Note :- There is no paper work has been done by my friend family. 

My Query :-  Q1 :- Is there is any Tax implication on any one in my friend family?

                     Q2 :- Is there is any documentation is required in this process?

                     Q3:-  If son transfer the money to his father saving bank account , Is there is any tax implication on son                                  or  father?