After Sita was sent away from Ayodhya by Rama, she lived in Sage Valmiki's ashram with her sons, Luv and Kush. The two boys grew up to be strong like their father, Rama.
One day, Rama held a big Ashvamedha Yajna. After the yajna, a sacred white horse was adorned with jewels and garments and it was declared that this horse would be taken around to many kingdoms across the region. A declaration was hung around the horse's neck, which stated that if anyone caught the horse, they would have to fight with the soldiers accompanying the horse. Shatrughna was entrusted with the task of taking the horse.
One day, the horse was passing by Sage Valmiki's ashram. Seeing the horse, Luv and Kush decided to take it to the ashram. While catching the horse, they noticed the declaration around its neck but were not in the least bit frightened. Soon, Shatrughna arrived with some soldiers and was furious to see that two young boys had caught the horse. He tried to persuade Luv and Kush to let the horse go but the boys were adamant and wanted to fight Satrughna's army.
Luv and Kush were very good at archery, and soon Shatrughana's soldiers fled and he had to accept defeat.
Shatrughana went back and told Rama about the young boys and how they had defeated the army. Rama asked Laxmana to go to Valmiki's ashram and get the horse back from the boys. He told Laxmana to bring the boys to Ayodhya.