SB 2.5.7

sa bhavān acarad ghoraṁ
 yat tapaḥ susamāhitaḥ
tena khedayase nas tvaṁ
 parā-śaṅkāṁ ca yacchasi
Word for word: 
saḥ — he; bhavān — your good self; acarat — undertook; ghoram — severe; yat tapaḥ — meditation; su-samāhitaḥ — in perfect discipline; tena — for that reason; khedayase — gives pain; naḥ — ourselves; tvam — your good self; parā — the ultimate truth; śaṅkām — doubts; ca — and; yacchasi — giving us a chance.
Translation: 
Yet we are moved to wonder about the existence of someone more powerful than you when we think of your great austerities in perfect discipline, although your good self is so powerful in the matter of creation.
Purport: 

Following in the footsteps of Śrī Nārada Muni, one should not blindly accept his spiritual master as God Himself. A spiritual master is duly respected on a par with God, but a spiritual master claiming to be God Himself should at once be rejected. Nārada Muni accepted Brahmā as the Supreme due to Lord Brahmā’s wonderful acts in creation, but doubts arose in him when he saw that Lord Brahmā also worshiped some superior authority. The Supreme is supreme, and He has no worshipable superior. The ahaṅgrahopāsitā, or the one who worships himself with the idea of becoming God Himself, is misleading, but the intelligent disciple can at once detect that the Supreme God does not need to worship anyone, including Himself, in order to become God. Ahaṅgrahopāsanā may be one of the processes for transcendental realization, but the ahaṅgrahopāsitā can never be God Himself. No one becomes God by undergoing a process of transcendental realization. Nārada Muni thought of Brahmājī as the Supreme Person, but when he saw Brahmājī engaged in the process of transcendental realization, doubts arose in him. So he wanted to be clearly informed.