Mbh 13.100.2c

Agastya also, though treated by Nahusha in this way, did not give way to wrath. Then, O Bharata, king Nahusha urged Agastya on with his goad. The righteous-souled Rishi did not still give way to anger. The lord of the deities, himself giving way to anger, then struck Agastya on the head with his left foot. When the Rishi was thus struck on the head, Bhrigu, who was staying within Agastya's matted locks, became incensed and cursed Nahusha of sinful soul, saying, 'Since thou hast struck with thy foot on the head of this great Rishi, do thou, therefore, fall down on the earth, transformed into a snake, O wretch of wicked understanding!' Thus cursed by Bhrigu who had not been seen, Nahusha immediately became transformed into a snake and fell down on the earth, O chief of Bharata's race! If O monarch, Nahusha had seen Bhrigu, the latter would not then have succeeded, by his energy, in hurling the former down on the earth. In consequence of the various gifts that Nahusha had made, as also his penances and religious observances though hurled down on the earth, O king, he succeeded in retaining his memory. He then began to propitiate Bhrigu with a view to the working out of the curse. Agastya also, filled with compassion, joined Nahusha in pacifying Bhrigu for bringing about an end of the curse. At last Bhrigu felt compassion for Nahusha and provided for the working out of the curse.