The Chapter on the Practices and Vows of Samantabhadra from the Avatamsaka Sutra (Traditional Chinese) - Sutra Tracing Series

The term "heart" (Sanskrit: hṛdaya) refers to the heart itself, but also carries meanings such as essence and core. This sutra distills the vast teachings of the Prajna Sutras into a concise classic, expressing the idea that "Prajna is emptiness." The entire text draws upon the Five Aggregates, the Threefold Division, the Twelve Causes and Conditions, and the Four Noble Truths to summarize the principle that all phenomena are empty. The well-known phrase "form is emptiness, emptiness is form" originates from this sutra.