Drops of Dundhubi's blood rained down upon the ashram, and Matanga grew angry. When he found Dundhubi's corpse lying on the ground, he shouted out a curse. "Whoever flung this corpse here will die if he sets foot on Rishyamukha Hill."
That is why, when Sugriva later fled from his brother Vali, he took refuge on Rishyamukha Hill. Vali feared the sage's curse, so Sugriva was safe from Vali there.
Inspired by: Valmiki's Ramayana
Notes: This is the Kishkindha Kanda (Book 4), sarga 11.