CC Madhya 20.112

viṣṇu-śaktiḥ parā proktā
kṣetrajñākhyā tathā parā
avidyā-karma-saṁjñānyā
tṛtīyā śaktir iṣyate
Synonyms: 
viṣṇu-śaktiḥ — the potency of Lord Viṣṇu; parā — spiritual; proktā — it is said; kṣetra-jña-ākhyā — the potency known as kṣetrajña; tathā — as well as; parā — spiritual; avidyā — ignorance; karma — fruitive activities; saṁjñā — known as; anyā — other; tṛtīyā — third; śaktiḥ — potency; iṣyate — known thus.
Translation: 
“ ‘Originally, Kṛṣṇa’s energy is spiritual, and the energy known as the living entity is also spiritual. However, there is another energy, called illusion, which consists of fruitive activity. That is the Lord’s third potency.’
Purport: 

This is a quotation from the Viṣṇu Purāṇa (6.7.61). For a further explanation of this verse, refer to Ādi-līlā, chapter seven, verse 119.