Mbh 3.291.3a

“Markandeya said, ‘Listen, O king, how the exalted merit of chaste ladies, O Yudhishthira, was completely obtained by a princess named Savitri. There was a king among the Madras, who was virtuous and highly pious. And he always ministered unto the Brahmanas, and was high-souled and firm in promise. And he was of subdued senses and given to sacrifices. And he was the foremost of givers, and was able, and beloved by both the citizens and the rural population. And the name of that lord of Earth was Aswapati. And he was intent on the welfare of all beings. And that forgiving (monarch) of truthful speech and subdued senses was without issue. And when he got old, he was stricken with grief at this. And with the object of raising offspring, he observed rigid vows and began to live upon frugal fare, having recourse to the Brahmacharya mode of life, and restraining his senses. And that best of kings, (daily) offering ten thousand oblations to the fire, recited Mantras in honour of Savitri[106] and ate temperately at the sixth hour. And he passed eighteen years, practising such vows. Then when the eighteen years were full, Savitri was pleased (with him). And O king, issuing with great delight, in embodied form, from the Agnihotra fire, the goddess showed herself to that king. And intent on conferring boons, she spoke these words unto the monarch, ‘I have been gratified, O king, with thy Brahmacharya practices, thy purity and self-restraint and observance of vows, and all thy endeavours and veneration! Do thou, O mighty king. O Aswapati, ask for the boon that thou desirest! Thou ought, however, by no means show any disregard for virtue.’ Thereat Aswapati said, ‘It is with the desire of attaining virtue that I have been engaged in this task. O goddess, may many sons be born unto me worthy of my race! If thou art pleased with me, O goddess, I ask for this boon. The twice-born ones have assured me that great merit lieth in having offspring!’