SB 11.15.22

yadā mana upādāya
 yad yad rūpaṁ bubhūṣati
tat tad bhaven mano-rūpaṁ
 mad-yoga-balam āśrayaḥ
Synonyms: 
yadā — when; manaḥ — the mind; upādāya — applying; yat yat — whatever; rūpam — form; bubhūṣati — one desires to assume; tat tat — that very form; bhavet — may appear; manaḥ-rūpam — the form desired by the mind; mat-yoga-balam — My inconceivable mystic potency, by which I manifest innumerable forms; āśrayaḥ — being the shelter.
Translation: 
When the yogī, applying his mind in a certain way, desires to assume a particular form, that very form immediately appears. Such perfection is possible by absorbing the mind in the shelter of My inconceivable mystic potency, by which I assume innumerable forms.
Purport: 

This perfection is called kāma-rūpa, or the ability to assume any form that one desires, even the form of a demigod. The pure devotees absorb their minds in a particular type of service to Lord Kṛṣṇa and thus gradually assume a spiritual body for an eternal life of bliss and knowledge. Thus anyone who takes to the process of chanting the holy names of Kṛṣṇa and follows the regulative principles of human life can acquire the ultimate perfection of kāma-rūpa, assuming an eternal, spiritual body in the kingdom of God.