Manjushri-mula-kalpa

The Mañjuśrī-mūla-kalpa is text of the class designated as Kriyā-tantra. It is closely aligned and identified with the bodhisattva Mañjuśrī.

This Mañjuśrī-mūla-kalpa is often cited as the earliest example of an extant Indian Buddhist Tantra. Some scholars identify it as a compilation of a core dated circa 6th century with accretions and additions.

The Sanskrit version, significantly longer than its corresponding Chinese and Tibetan renderings, is still extant.

The Mañjusrimulakalpa, which later came to classified under Kriyatantra, states that mantras taught in the Shaiva, Garuda and Vaishnava tantras will be effective if applied by Buddhists since they were all taught originally by Manjushri.

...
Wikipedia