Mahabharata Adi Parva Chapter 106:2

Mahabharata Adi Parva Chapter 106:2 "Some time after, when the oldest of Vichitravirya's widows again had her monthly season, she was solicited by Satyavati to approach Vyasa once again. Possessed of beauty like a daughter of a celestial, the princess refused to do her mother-in-law's bidding, remembering the grim visage and strong odour of the Rishi. She, however, sent unto him, a maid of hers, endued with the beauty of an Apsara and decked with her own ornaments. And when the Vyasa arrived, the maid rose up and saluted him. And she waited upon him respectfully and took her seat near him when asked. And, O king, the great Rishi of rigid vows, was well-pleased with her, and when he rose to go away, he addressed her and said, 'Amiable one, thou shalt no longer be a slave. Thy child also shall be greatly fortunate and virtuous, and the foremost of all intelligent men on earth!' And, O king, the son thus begotten upon her by Krishna-Dwaipayana was afterwards known by the name of Vidura. He was thus the brother of Dhritarashtra and the illustrious Pandu. And Vidura was free from desire and passion and was conversant with the rules of government, and was the god of justice born on earth under the curse of the illustrious Rishi Mandavya. And Krishna-Dwaipayana, when he met his mother as before, informed her as to how he had been deceived by the seniormost of the princesses and how he had begotten a son upon a Sudra woman. And having spoken thus unto his mother the Rishi disappeared from her sight. "Thus were born, in the field of Vichitravirya, even of Dwaipayana those sons of the splendour of celestial children, those propagators of the Kuru race.'"