Mahabharata Anushasna Parva Chapter 141:7

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 141:7 He never resides in the same place for more than a day. Freed from all bonds he roves over the world. Emancipated from all ties, he never sleeps on even the same river-bank for more than a day. Even this is the religion of persons conversant with Emancipation as declared in the Vedas. Even this is the righteous path that is trodden by the righteous. He who follows in this track leaves no vestige behind. Bhikshus (or followers of the religion of Emancipation) are of four kinds. They are Kutichakas, Vahudakas, Hansas, and Paramahansas. The second is superior to the first, the third to the second, and the fourth to the third. There is nothing superior to the Paramahansa; nor is there anything inferior to it or beside it or before it. It is a condition that is divested of sorrow and happiness; that is auspicious and freed from decrepitude and death and that knows no change."[] 'Uma said, "Thou hast recited the religion of the householders, that of Emancipation, and that which is based upon the observances of the righteous. These paths are high and exceedingly beneficial to the world of living creatures. O thou that art conversant with every religion, I desire now to hear what is the high religion of the Rishis. I always have a liking for those that dwell in ascetic retreats. The perfume that emanates from the smoke of the libations of clarified butter poured on the sacred fire seems to pervade the entire retreats and make them delightful. Marking this, O great god, my heart becomes always filled with delight. O puissant deity, I have doubts regarding the religion of the ascetics. Thou art conversant with the details of all religions. Do thou enlighten me, O god of gods, in detail, respecting this topic truly about which I have asked thee, O great deity!" 'The blessed and holy one said, "Yes, I shall recite to thee the high and excellent religion of the ascetics. By following the dictates of that religion, O auspicious lady, the ascetics attain to success through the severe penances they practise. O highly blessed one, do thou hear, from the beginning, what the duties are of those righteous Rishis that are conversant with every duty and that are known by the name of Phenapas. The Grandsire Brahma (during the days he devoted to the observance of penances) drank some nectar (in the form of water). That water had flowed in heaven from a great sacrifice. The froth of that water is highly auspicious and (in consequence of Brahma's having drunk it) it partook of His own nature. Those Rishis that subsist upon the measure of froth that thus issued (from the water indicated) are called Phenapas (Froth-eaters). Even this is the conduct of those pure-souled Rishis, O lady, possessed of wealth of penances! Listen now to me as I explain to thee who the Valkhilyas are. The Valkhilyas are ascetics that have won success by their penances. They reside in the solar disc.