No such clarification from the Income Tax Department. Only a rent receipt is required for claiming HRA.
For let-out properties, the Income Tax Department generally does not ask for agreements. Only in the case of scrutiny matters, they ask for an agreement or confirmation from the tenant.
The Department has not prescribed anything specific about a rent agreement for determining income from house property. The information required for this purpose includes rent actually receivable for the year, municipal value, standard rent as may have been determined by the Rent Control Authorities, and the fair rent the property would fetch.