Bhagavad-gītā 10.6

The Lord is giving a genealogical synopsis of the universal population. Brahmā is the original creature born out of the energy of the Supreme Lord, who is known as Hiraṇyagarbha. And from Brahmā all the seven great sages, and before them four other great sages, named Sanaka, Sananda, Sanātana and Sanat-kumāra, and the fourteen Manus, are manifested. All these twenty-five great sages are known as the patriarchs of the living entities all over the universe. There are innumerable universes and innumerable planets within each universe, and each planet is full of population of different varieties. All of them are born of these twenty-five patriarchs. Brahmā underwent penance for one thousand years of the demigods before he realized by the grace of Kṛṣṇa how to create. Then from Brahmā came Sanaka, Sananda, Sanātana and Sanat-kumāra, then Rudra, and then the seven sages, and in this way all the brāhmaṇas and kṣatriyas are born out of the energy of the Supreme Personality of Godhead. Brahmā is known as Pitāmaha, the grandfather, and Kṛṣṇa is known as Prapitāmaha, the father of the grandfather. That is stated in the Eleventh Chapter of the Bhagavad-gītā (BG 11.39, Available in the library).