In this news clip from WION, the anchor is saying that when Lord Rama came back to Ayodhya, the residents of Ayodhya decorated their houses with lamps. That is how the festival of Diwali (Deepavali) began. I heard this narration in many other places as well. Even the accepted answer of the post (What is the significance of the festival Diwali? Why is it celebrated?) from the Hinduism Stack Exchange also tell us the same thing. It has two links related to Ramayana. Both links are Wikipedia articles. and there is no mention of Diwali or Deepavali.
I want to know whether Diwali was mentioned in the Valmiki Ramayana. Please cite relevant verses from Valmiki Ramayana.