Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 13
Sanskrit:
जन्मना जनक: सोऽभूद् वैदेहस्तु विदेहज: ।मिथिलो मथनाज्जातो मिथिला येन निर्मिता ॥ १३ ॥
ITRANS:
janmanā janakaḥ so ’bhūdvaidehas tu videhajaḥmithilo mathanāj jātomithilā yena nirmitā
Translation:
Because he was born in an unusual way, the son was called Janaka, and because he was born from the dead body of his father, he was known as Vaideha. Because he was born from the churning of his father’s material body, he was known as Mithila, and because he constructed a city as King Mithila, the city was called Mithilā.