Srimad Bhagavatam Canto 01, Chapter 15, Text 35

SB 1.15.35

yatha matsyadi-rupani
dhatte jahyad yatha natah
bhu-bharah ksapito yena
jahau tac ca kalevaram
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The Supreme Lord relinquished the body which He manifested to diminish the burden of the earth. Just like a magician, He relinquishes one body to accept different ones, like the fish incarnation and others.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The Supreme Lord Personality of Godhead is neither impersonal nor formless, but His body is nondifferent from Him, and therefore He is known as the embodiment of eternity, knowledge and bliss. In the Brhad-vaisnava Tantra it is clearly mentioned that anyone who considers the form of Lord Krsna to be made of material energy must be ostracized by all means. And if by chance the face of such an infidel is seen, one must clean himself by jumping in the river with his clothing. The Lord is described as amrta, or deathless, because He has no material body. Under the circumstances, the Lord’s dying or quitting His body is like the jugglery of a magician. The magician shows by his tricks that he is cut to pieces, burnt to ashes or made unconscious by hypnotic influences, but all are false shows only. Factually the magician himself is neither burnt to ashes nor cut to pieces, nor is he dead or unconscious at any stage of his magical demonstration. Similarly, the Lord has His eternal forms of unlimited variety, of which the fish incarnation, as was exhibited within this universe, is also one. Because there are innumerable universes, somewhere or other the fish incarnation must be manifesting His pastimes without cessation. In this verse, the particular word dhatte (“eternally accepted,” and not the word dhitva, “accepted for the occasion”) is used. The idea is that the Lord does not create the fish incarnation; He eternally has such a form, and the appearance and disappearance of such an incarnation serves particular purposes. In the Bhagavad-gita (7.24-25) the Lord says, “The impersonalists think that I have no form, that I am formless, but that at present I have accepted a form to serve a purpose, and now I am manifested. But such speculators are factually without sharp intelligence. Though they may be good scholars in the Vedic literatures, they are practically ignorant of My inconceivable energies and My eternal forms of personality. The reason is that I reserve the power of not being exposed to the nondevotees by My mystic curtain. The less intelligent fools are therefore unaware of My eternal form, which is never to be vanquished and is unborn.” In the Padma Purana it is said that those who are envious and always angry at the Lord are unfit to know the actual and eternal form of the Lord. In the Bhagavatam also it is said that the Lord appeared like a thunderbolt to those who were wrestlers. Sisupala, at the time of being killed by the Lord, could not see Him as Krsna, being dazzled by the glare of the brahmajyoti. Therefore, the temporary manifestation of the Lord as a thunderbolt to the wrestlers appointed by Kamsa, or the glaring appearance of the Lord before Sisupala, was relinquished by the Lord, but the Lord as a magician is eternally existent and is never vanquished in any circumstance. Such forms are temporarily shown to the asuras only, and when such exhibitions are withdrawn, the asuras think that the Lord is no more existent, just as the foolish audience thinks the magician to be burnt to ashes or cut to pieces. The conclusion is that the Lord has no material body, and therefore He is never to be killed or changed by His transcendental body.
Srimad Bhagavatam Canto 01, Chapter 15, Text 34
Srimad Bhagavatam Canto 01, Chapter 15, Text 36