CC Madhya 24.74
tattvaṁ yaj jñānam advayam
bhagavān iti śabdyate
“ ‘Learned transcendentalists who know the Absolute Truth say that it is nondual knowledge and is called impersonal Brahman, localized Paramātmā and the Personality of Godhead.’
This is a quotation from Śrīmad-Bhāgavatam (1.2.11). For an explanation, see Ādi-līlā 2.11.