Srimad Bhagavatam Canto 11, Chapter 16, Text 32

SB 11.16.32

ojah saho balavatam
 karmaham viddhi satvatam
satvatam nava-murtinam
 adi-murtir aham para
 
Translation: 
 
Of the powerful I am bodily and mental strength, and I am the devotional activities of My devotees. My devotees worship Me in nine different forms, among which I am the original and primary Vasudeva.
 
Purport: 
 
Generally, the Vaisnavas worship the Personality of Godhead as Vasudeva, Sankarsana, Pradyumna, Aniruddha, Narayana, Hayagriva, Varaha, Nrsimha and Brahma. It is understood that when a suitable living entity is not available to fill the post of Brahma, the Lord Himself assumes the position; therefore Lord Brahma is mentioned in the list. Lord Visnu sometimes appears as Indra and sometimes as Brahma, and it is Visnu appearing as Brahma who is indicated in this connection.
Srimad Bhagavatam Canto 11, Chapter 16, Text 31
Srimad Bhagavatam Canto 11, Chapter 16, Text 33