Rama had promised Sugriva, the monkey king, that he will
defeat Vali for him. But Sugriva doubted whether Sri Ram will be able to defeat
the powerful Vali. To give an idea about the strength of Vali, Sugriva narrates
him the story of how Vali defeated demon Dundubhi. Sugriva then gives two
tests to Bhagvan Sri Ram.
First test is to lift the skeleton of Dundubhi with foot and
fling it to a distance. Rama walked up to the huge skeleton of Dundubhi and
lifted it with his toe and flung to a huge distance.
Next Sugriva asked Him to pierce seven sala trees with seven
arrows as this feat was performed by Vali.
Sri Ram took a single arrow. He pulled the single arrow and
released it. It pierced all the seven sala trees and returned to the quiver of
Rama.
Sugriva was jubilant and his doubts regarding the strength
of Rama were cleared.
This story is found in the Kishkinda Kanda of Ramayana.