Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 5
ब्रह्मादयो लोकनाथा: स्वनाथाय समादृता: ।सानुगा बलिमाजह्रु: सङ्क्षिप्तात्मविभूतये ॥ ५ ॥
brahmādayo loka-nāthāḥsva-nāthāya samādṛtāḥsānugā balim ājahruḥsaṅkṣiptātma-vibhūtaye
Lord Brahmā and all the predominating deities of the various planetary systems began to worship Lord Vāmanadeva, their supreme master, who had reduced Himself from His all-pervading form to His original form. They collected all the ingredients and paraphernalia for this worship.
Vāmanadeva first expanded Himself to the universal form and then reduced Himself to the original Vāmana-rūpa. Thus He acted exactly like Lord Kṛṣṇa, who, at the request of Arjuna, first showed His universal form and later resumed His original form as Kṛṣṇa. The Lord can assume any form He likes, but His original form is that of Kṛṣṇa (kṛṣṇas tu bhagavān svayam). According to the capacity of the devotee, the Lord assumes various forms so that the devotee can handle Him. This is His causeless mercy. When Lord Vāmanadeva resumed His original form, Lord Brahmā and his associates collected various paraphernalia for worship with which to please Him.