Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 12

Sanskrit:

यद्यप्यसावधर्मेण मां बध्नीयादनागसम् ।तथाप्येनं न हिंसिष्ये भीतं ब्रह्मतनुं रिपुम् ॥ १२ ॥

ITRANS:

yadyapy asāv adharmeṇamāṁ badhnīyād anāgasamtathāpy enaṁ na hiṁsiṣyebhītaṁ brahma-tanuṁ ripum

Translation:

Although He is Viṣṇu Himself, out of fear He has covered Himself in the form of a brāhmaṇa to come to me begging. Under the circumstances, because He has assumed the form of a brāhmaṇa, even if He irreligiously arrests me or even kills me, I shall not retaliate, although He is my enemy.

Purport:

If Lord Viṣṇu as He is had come to Bali Mahārāja and asked him to do something, Bali Mahārāja certainly would not have refused His request. But to enjoy a little humor between Himself and His devotee, the Lord covered Himself as a brāhmaṇa-brahmacārī and thus came to Bali Mahārāja to beg for only three feet of land.