When the defeated demons (the snakes who live in the planetary system known as Mahatala) met the female messenger Sarama, who was chanting a mantra, they became afraid, and therefore they are living in the planet called Rasatala

Expressions researched:
"When the defeated demons met the female messenger Sarama, who was chanting a mantra, they became afraid, and therefore they are living in the planet called Rasatala"

Srimad-Bhagavatam

SB Canto 5

It is said that there was a great fight between these serpentine demons and Indra, the King of heaven. When the defeated demons met the female messenger Saramā, who was chanting a mantra, they became afraid, and therefore they are living in the planet called Rasātala.

SB 5.24.30, Translation and Purport

Beneath Mahātala is the planetary system known as Rasātala, which is the abode of the demoniac sons of Diti and Danu. They are called Paṇis, Nivāta-kavacas, Kāleyas and Hiraṇya-puravāsīs [those living in Hiraṇya-pura]. They are all enemies of the demigods, and they reside in holes like snakes. From birth they are extremely powerful and cruel, and although they are proud of their strength, they are always defeated by the Sudarśana cakra of the Supreme Personality of Godhead, who rules all the planetary systems. When a female messenger from Indra named Saramā chants a particular curse, the serpentine demons of Mahātala become very afraid of Indra.

It is said that there was a great fight between these serpentine demons and Indra, the King of heaven. When the defeated demons met the female messenger Saramā, who was chanting a mantra, they became afraid, and therefore they are living in the planet called Rasātala.