Srimad Bhagavatam Canto 10, Chapter 11, Text 41

SB 10.11.41

kadacid yamuna-tire
vatsams carayatoh svakaih
vayasyaih krsna-balayor
jighamsur daitya agamat
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
One day while Rama and Krsna, along with Their playmates, were tending the calves on the bank of the river Yamuna, another demon arrived there, desiring to kill Them.
Srimad Bhagavatam Canto 10, Chapter 11, Text 39-40
Srimad Bhagavatam Canto 10, Chapter 11, Text 42