Bṛhad-bhāgavatāmṛta Part 2 Chapter 2 Text 146

ittham ahnāṁ katipaye
prayāte prātar ekadā
kautukād brahmaṇā spṛṣṭaḥ
pheṇa-puñjo ’suro ’bhavatTRANSLATION
After I had spent some days in this way, early one morning, out of curiosity, Brahmā touched a mass of foam, and it turned into a demon.