In Ramanada Sagar's adaptation of the Ramayana whenever some yajna is performed, I can hear background recital of some verses which is repeated again and again. In the below video, at ~18:10 mins Vishwamitra is interuppted by Marich and Subahu when the former starts a yajna here once can hear the verse in chorus.
I listen it unintelligibly as:
Vedaputra/Devaputra samvato vrikshnatma yajaamaha Indraya vischtai ?????? Indraya putri?? sandwawa?
Could any tell me from which book and what verse is being recited here