Srimad Bhagavatam Canto 10, Chapter 13, Text 15

SB 10.13.15

ambhojanma-janis tad-antara-gato mayarbhakasyesitur
drastum mañju mahitvam anyad api tad-vatsan ito vatsapan
nitvanyatra kurudvahantaradadhat khe ’vasthito yah pura
drstvaghasura-moksanam prabhavatah praptah param vismayam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
O Maharaja Pariksit, Brahma, who resides in the higher planetary system in the sky, had observed the activities of the most powerful Krsna in killing and delivering Aghasura, and he was astonished. Now that same Brahma wanted to show some of his own power and see the power of Krsna, who was engaged in His childhood pastimes, playing as if with ordinary cowherd boys. Therefore, in Krsna’s absence, Brahma took all the boys and calves to another place. Thus he became entangled, for in the very near future he would see how powerful Krsna was.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
When Aghasura was being killed by Krsna, who was accompanied by His associates, Brahma was astonished, but when he saw that Krsna was very much enjoying His pastimes of lunch, he was even more astonished and wanted to test whether Krsna was actually there. Thus he became entangled in Krsna’s maya. After all, Brahma was born materially. As mentioned here, ambhojanma janih: he was born of ambhoja, a lotus flower. It does not matter that he was born of a lotus and not of any man, animal or material father. A lotus is also material, and anyone born through the material energy must be subject to the four material deficiencies: bhrama (the tendency to commit mistakes), pramada (the tendency to be illusioned), vipralipsa (the tendency to cheat) and karanapatava (imperfect senses). Thus Brahma also became entangled.
Brahma, with his maya, wanted to test whether Krsna was actually present. These cowherd boys were but expansions of Krsna’s personal self (ananda-cinmaya-rasa-pratibhavitabhih). Later Krsna would show Brahma how He expands Himself into everything as His personal pleasure, ananda-cinmaya-rasa. Hladini saktir asmat: Krsna has a transcendental potency called hladini sakti. He does not enjoy anything that is a product of the material energy. Brahma, therefore, would see Lord Krsna expand His energy.
Brahma wanted to take away Krsna’s associates, but instead he took away some other boys and calves. Ravana wanted to take away Sita, but that was impossible, and instead he took away a maya Sita. Similarly, Brahma took away mayarbhakah: boys manifested by Krsna’s maya. Brahma could show some extraordinary opulence to the mayarbhakah; but he could not show any extraordinary potency to Krsna’s associates. That he would see in the very near future. Mayarbhakasya isituh. This bewilderment, this maya, was caused by the supreme controller, prabhavatahthe all-potent Supreme Person, Krsnaand we shall see the result. Anyone materially born is subject to bewilderment. This pastime is therefore called brahma-vimohana-lila, the pastime of bewildering Brahma. Mohitam nabhijanati mam ebhyah param avyayam (Bg. 7.13). Materially born persons cannot fully understand Krsna. Even the demigods cannot understand Him (muhyanti yat surayah). Tene brahma hrda ya adi-kavaye (Bhag. 1.1.1). Everyone, from Brahma down to the small insect, must take lessons from Krsna.
Srimad Bhagavatam Canto 10, Chapter 13, Text 14
Srimad Bhagavatam Canto 10, Chapter 13, Text 16