In the Bhagavad-gītā there is another instance. When Arjuna asked Kṛṣṇa, Kṛṣṇa said, imaṁ vivasvate yogaṁ proktavān aham avyayam [Bg. 4.1]. Kṛṣṇa said that, "First of all, I narrated this yoga system of Bhagavad-gītā to the sun-god." So, in order to clear this matter, Arjuna inquired from Him: "My dear Kṛṣṇa, we are born very recently. How is that You narrated this yoga system to the sun-god?" Arjuna, of course, knew everything, but in order to clear our doubts, he raised this question. And Kṛṣṇa answered that "You were also present at that time, but you have forgotten. I have not forgotten." So this is another proof that Kṛṣṇa, Kṛṣṇa's body does not change. Kṛṣṇa, when He comes, when He appears, He comes in His original spiritual body. Therefore Kṛṣṇa has warned that avajānanti māṁ mūḍhāḥ [Bg. 9.11].
The Māyāvādī philosophers who think that Kṛṣṇa has accepted a material body, they are described as mūḍhas. They have no sufficient knowledge. Paraṁ bhāvam ajānantaḥ. They do not know what is the power behind Kṛṣṇa. So Kṛṣṇa creates. Before creation, aham ādir hi devānām [Bg 10.2]. In the Bhagavad-gītā it is said, devānām. First of all, Brahmā was created. Then other great sages were created. Then other demigods were created. But Kṛṣṇa says, aham ādir hi devānām. Therefore He's not a created being of this material world. We have to consider in that way. Ahaṁ sarvasya prabhavo mattaḥ sarvaṁ pravartate [Bg. 10.8]. The Vedānta-sūtra: janmādy asya yataḥ [SB 1.1.1]. So Kṛṣṇa is the origin of everything. Ahaṁ sarvasya prabhavaḥ [Bg. 10.8]. Iti matvā bhajante māṁ budhā bhāva-samanvitāḥ. One who knows Kṛṣṇa, the Supreme, ādi-puruṣam, ādyaṁ purāṇa-puruṣaṁ nava-yauvanaṁ ca [Bs. 5.33], his knowledge is perfect. If one thinks Kṛṣṇa as one of the products of this material word, then his knowledge is imperfect. He's still in the darkness of this material creation.
Prabhupada's lecture - Śrīmad-Bhāgavatam 1.2.30 - Vṛndāvana, November 9, 1972