Mahabharata Santi Parva Chapter 341:3

Mahabharata Santi Parva (Mokshadharma Parva) Chapter 341:3 Marichi, Angiras, Atri, Pulastya, Pulaha, Kratu, the high-souled Vasishtha, and the Self-born Manu, these should be known as the eight Prakritis. Upon these rest all the worlds. Then the Grandsire of all the world, viz., Brahman, created, for the fulfilment of all creatures, the Vedas with all their branches, as also the Sacrifices with their limbs. From these eight Prakritis have sprung this vast universe. Then sprang Rudra from the principle of wrath, starting into life, he created ten others that were like him. These eleven Rudras are called by name of Vikara-Purushas. The Rudras, the (eight) Prakritis, and the several celestial Rishis, having started into life, approached Brahman with the object of upholding the universe and its operations. Addressing the Grandsire, they said, 'We have been created, O holy one, by thee, O thou of great puissance. Tell each of us, O Grandsire, the respective jurisdiction we shall be vested with. What particular jurisdictions have been created by thee for supervising the different affairs? We, each, should be endued with what kind of consciousness and shall take charge of which of these? Do thou ordain also unto each of us the measure of strength that we are to have for discharging the duties of our respective jurisdictions.' Thus addressed by them, the great god replied unto them in the following way. Brahman said, 'You have done well, ye deities, in speaking to me of this matter. Blessed be you all! I was thinking of this very subject that has engaged your attention. How should the three worlds be upheld and kept agoing? How should your strength and mine be utilized towards that end? Let all of us, leaving this place, repair to that unmanifest and foremost of Beings who is the witness of the world, for seeking his protection. He will tell us what is for our good.' After this, those deities and Rishis, with Brahman, proceeded to the northern shores of the Ocean of milk, desirous of doing good to the three worlds. Arrived there, they began to practise those austere penances that are declared by Brahman in the Vedas. Those austerest of penances are known by the name of Mahaniyama (the foremost vows and observances). They stood there with mind fixed, immovable as posts of wood, and with eyes upturned and arms raised upwards. For a thousand celestial years they were engaged in those severe penances. At the conclusion of that period they heard these sweet words in harmony with the Vedas and their branches. The blessed and holy one said, 'Ye deities and Rishis possessed of wealth of asceticism, with Brahman in your company, after according you all welcome, I say unto you these words. I know that is in your hearts. Verily, the thoughts that engage you are for the good of the three worlds. I shall increase your energy and strength investing the same with Pravritti (predilection for acts). Ye gods, well have you undergone these penances from desire of adoring me. Ye foremost of Beings, enjoy now the excellent fruits of austerities which ye have gone through. This Brahman is the Lord of all the worlds.