Transfer of tenancy rights - Pagdi House Mumbai

We have given up our tenancy rights of our pagdi house in Mumbai. For that we have received xxx amount from the new tenant and the landlord took xxx amount to transfer the tenancy rights. The landlord refused to go ahead with the registration and he just transferred the rent receipt in the new tenants name. We handed an affidavit stating that we are handing over the possession to the new tenant and we have no objections to it. The landlord kept the original copy of the same. Now I would like to know the necessary documents we as seller need to keep in our possession for income tax purpose. Since we have received XXX amount in cheque and there is no document stating or proving for what the amount is received we would like to know the procedure we need to follow. We understand that the entire amount received will be considered as Long Term Capital Gain hence we plan to invest it in Long Term Capital bonds under section 54EC of the IT act. Please do let me know if we need to have a notarised document signed by us(seller) and new tenant stating the transaction. And will this suffice if we ever happen to receive any query at a later stage from the Income Tax department.