To satisfy the sage Utaṅka, the greatly powerful Kuvalayāśva killed a demon named Dhundhu. He did this with the assistance of his twenty-one thousand sons.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यः प्रियार्थमुतङ्कस्य धुन्धुनामासुरं बली । सुतानामेकविंशत्या सहस्रैरहनद्वृतः
yaḥ priyārthamutaṅkasya dhundhunāmāsuraṃ balī | sutānāmekaviṃśatyā sahasrairahanadvṛtaḥ
SB 9.6.22