Am I liable to refund 1 crore to the buyer without a completion date or written agreement?

I seek your guidance as an Indian lawyer regarding a situation involving my father. He agreed to sell our house for 1.65 crore on June 28, 2019. As of now (March 8, 2024), there is no completion date specified in the agreement. The buyer has paid a sum of 1 crore in installments, and their family has been residing in the house since August 2019. Recently, the buyer has requested a refund of the 1 crore, citing financial constraints preventing them from completing the purchase. The primary reason my father intended to sell the house was due to a 1 crore home loan, with monthly installments of 110,000. Unfortunately, he encountered difficulties meeting these payments, prompting the decision to sell the property. The buyer was aware of this situation and, upon providing a token amount on June 28, assured my father that the full payment would be made within three months to help settle the loan. However, to date, the buyer has not fulfilled this commitment. I would like to clarify whether I am legally liable to repay the 1 crore to the buyer. Additionally, it's important to note that there is no written documentation confirming the payment made. I seek your guidance on the appropriate course of action in this circumstance.