What is the name f the first texts that mentioned Tantra?

The first texts that mentioned Tantra are primarily the "Vedas" and later the "Upanishads." However, the specific and more detailed exposition of Tantra is found in texts like the "Tantras" themselves, particularly the "Kularnava Tantra" and the "Mahanirvana Tantra." These texts emerged around the 5th to 9th centuries CE, outlining rituals, philosophy, and practices associated with Tantric traditions.