Emperor Harsha refers to Deepavali in the 7th-century Sanskrit play Nagananda.
Nagananda is a five-act Sanskrit drama attributed to Harsha, who ruled much of northern India from 606 to 648 CE. The play tells the story of Jimutavahana, a prince who offers himself to Garuda to save a Naga from sacrifice. Its unusual Buddhist invocation, alongside its Hindu dramatic setting, has made it an important work in the history of Sanskrit theatre.
In Nagananda, Harsha uses the expression Dipapratipadotsava for the festival. The term combines words connected with lamps, the first lunar day, and celebration. The passage describes lamps being lit and newly married or engaged couples receiving gifts, providing evidence that festive illumination and gift-giving were established traditions in early medieval India.
The answer is sometimes confused with later literary references. Rajasekhara used Dipamalika in the 9th-century Kavyamimamsa, while Al-Biruni described the festival in an 11th-century account of India. Those are separate sources and periods.