Matsyapurana 175.48

175.48

ūrvastu tapasāviṣṭo niveśyoruṃ hutāśane
mamanthaikena darbheṇa sutasya prabhavāraṇim //

The ascetics ought to beget progeny out of the embryo created by their mind, and your address to me is bereft of dharma, and is like the speech of those who are not good By the power of my innerself, I shall create a son without the help of a woman, after illumining my mind with the glory of asceticism I shall create such a son out of my soul, who would be ready to consume the creation—44-47 Afterwards the sage Ūrva, absorbed in his asceticism, throwing his thighs into the fire rubbed them with a kûśa grass Then the son in the form of Fire, desirous of consuming the universe, was produced from his thigh, by its own force without the help of any firewood In such a way the fearful fire Aurvâ was begotten from the thigh of the seer Ūrva.—48-50