Devibhagavatapurana 3.28.6

3.28.6

sūnavaḥ kṛtasaṃskārā bhūpateḥ sukhavardhakāḥ |
kauśikena tadā''gatya prārthito raghunandanaḥ ||

Thus educated and purified, the four sons began to give delight more and more to the king; one day the Maharsi Vis’vâmitra came to Ayodhyâ and aked from the king Das’aratha the help of his son Râmachandra for the protection of his sacrificial ceremonies. The king could not cancel the Vis’vâmitra's request and sent with him Râma, accompanied by Laksmana.