SB 10.24.35

kṛṣṇas tv anyatamaṁ rūpaṁ
 gopa-viśrambhaṇaṁ gataḥ
śailo ’smīti bruvan bhūri
 balim ādad bṛhad-vapuḥ
Synonyms: 
kṛṣṇaḥ — Lord Kṛṣṇa; tu — and then; anyatamam — another; rūpam — transcendental form; gopa-viśrambhaṇam — for generating the faith of the cowherds; gataḥ — assumed; śailaḥ — the mountain; asmi — I am; iti — these words; bruvan — saying; bhūri — abundant; balim — the offerings; ādat — He devoured; bṛhat-vapuḥ — in His huge form.
Translation: 
Kṛṣṇa then assumed an unprecedented, huge form to instill faith in the cowherd men. Declaring “I am Govardhana Mountain!” He ate the abundant offerings.
Purport: 

In Chapter Twenty-four of Kṛṣṇa, the Supreme Personality of Godhead, Śrīla Prabhupāda writes: “When everything was complete, Kṛṣṇa assumed a great transcendental form and declared to the inhabitants of Vṛndāvana that He was Himself Govardhana Hill in order to convince the devotees that Govardhana Hill and Kṛṣṇa Himself are identical. Then Kṛṣṇa began to eat all the food offered there. The identity of Kṛṣṇa and Govardhana Hill is still honored, and great devotees take rocks from Govardhana Hill and worship them exactly as they worship the Deity of Kṛṣṇa in the temples. The followers of the Krsna consciousness movement may therefore collect small rocks or pebbles from Govardhana Hill and worship them at home, because this worship is as good as Deity worship.”

Lord Kṛṣṇa had induced the residents of Vṛndāvana to assume a significant risk on His behalf. He convinced them to neglect a sacrifice to what is, after all, the powerful government of the universe and to worship a hill called Govardhana instead. The cowherd community did all this simply out of love for Kṛṣṇa, and now to convince them that their decision was correct, Lord Kṛṣṇa appeared in an unprecedented, huge transcendental form and demonstrated that He Himself was Govardhana Hill.