SB 8.1.2
manvantare harer janma
karmani ca mahiyasah
grnanti kavayo brahmams
tani no vada srnvatam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O learned brahmana, Sukadeva Gosvami, the great learned persons who are completely intelligent describe the activities and appearance of the Supreme Personality of Godhead during the various manvantaras. We are very eager to hear about these narrations. Kindly describe them.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Supreme Personality of Godhead has different varieties of incarnations, including the guna-avataras, manvantara-avataras, lila-avataras and yuga-avataras, all of which are described in the sastras. Without reference to the sastras there can be no question of accepting anyone as an incarnation of the Supreme Personality of Godhead. Therefore, as especially mentioned here, grnanti kavayah: the descriptions of various incarnations are accepted by great learned scholars with perfect intelligence. At the present time, especially in India, so many rascals are claiming to be incarnations, and people are being misled. Therefore, the identity of an incarnation should be confirmed by the descriptions of the sastras and by wonderful activities. As described in this verse by the word mahiyasah, the activities of an incarnation are not ordinary magic or jugglery, but are wonderful activities. Thus any incarnation of the Supreme Personality of Godhead must be supported by the statements of the sastra and must actually perform wonderful activities. Pariksit Maharaja was eager to hear about the Manus of different ages. There are fourteen Manus during a day of Brahma, and the age of each Manu lasts for seventy-one yugas. Thus there are thousands of Manus during the life of Brahma.