Why are certain important verses quoted by acharyas not found in the scriptures?
Devotee-scholars’ research is uncovering the presence in scripture of many verses whose sources were earlier unknown or debated. One excellent sample of such scholarship is this document compiled by a devotee-scholar and friend Hari Parshad Prabhu:
Prabhupada verses – sources found by Hari Parshad P
Specific reference to verses about Mayavada:
mayavadam asac chastram (sastram) pracchannam bauddham ucyate mayaiva kathyate devi kalau brahmana rupina
Also
vedante tu maha sastre mayavadam avaidikam mayaiva vaksyate devi jagatam nasa karanat
vedānte tu mahā śāstre māyāvādam avaidikam mayaiva vakṣyate devi jagatāṁ nāśa kāraṇāt
Quoted by Srila Jiva Goswami in Paramatma Sandarbha, and by other Gaudiya Vaishnava Acharyas in many other places.
Found in Padma Purana, 6 (Uttara Khanda), Chapter 236, Verse 5-6 and Verse 9-10
Published by Khemraj ShriKrishnaDas in Venkateshwar Steam Press, Khetwadi, Mumbai. 1927 A.D.
Sanskrit scan of the verse