SB 10.69.38

vidāma yoga-māyās te
 durdarśā api māyinām
yogeśvarātman nirbhātā
 bhavat-pāda-niṣevayā
Word for word: 
vidāma — we know; yoga-māyāḥ — the mystic potencies; te — Your; durdarśāḥ — impossible to see; api — even; māyinām — for great mystics; yoga-īśvara — O Lord of all mystic power; ātman — O Supreme Soul; nirbhātāḥ — perceived; bhavat — Your; pāda — to the feet; niṣevayā — by service.
Translation: 
[Nārada said:] Now we understand Your mystic potencies, which are difficult to comprehend, even for great mystics, O Supreme Soul, master of all mystic power. Only by serving Your feet have I been able to perceive Your powers.
Purport: 

According to the ācāryas, this verse indicates that even great mystics like Lord Brahmā and Lord Śiva cannot fully comprehend the mystic power of the Supreme Lord.