Looking for the source of a quote

[Rory94]

Several websites and books have proposed that "buddhatvam yosityonisamasritam" (or slight variants) are either the genuine words of the Buddha, or of later Tantric Buddhists.

The first claim is obviously false; while the second doesn't seem to have much basis in fact either.

The earliest source I've found for the quote is in de La Vallee-Poussin's 'Une Pratique des Tantres" (1897). He doesn't reference the text, however, though in the same passage of writing he does talk about the Candamaharosanatantra. This has led me to believe that he was misinterpreting chapter 10, verse 24: "caṇḍaroṣapadaṃ dṛṣṭvā yoṣidyonisamāśritam".

He's evidently a fine scholar; but fine scholars also make mistakes.

Anyone have any thoughts on this?