From "India" by Al-Beruni, page 100-101
"The distance from Panjayavar to Ramsher (Rameshar, Rameshwaram?)
is 40 farsakh, that between Ramsher and Setubandha 2 farsakh.
Setubandha means bridge of the ocean.
It is the dike of Rama, the son of Dasaratha,
which he built from the continent to the castle Lanka.
At present it consists of isolated mountains between which the ocean flows.
Sixteen farsakh from Setubandha towards the east is
Kihkind the mountain of the monkey.
Every day the king of monkeys comes out of the thicket together with his hosts,
and settles down in particular seats prepared for them.
The inhabitants of that region prepare for them cooked rice,
and bring it to them on leaves.
After having eaten it they return into the thicket,
but in case they are neglected, this would be the ruin of the country,
as they are not only numerous but also savage and aggressive.
According to the popular belief,
they are a race of men changed into monkeys
on account of the help which they had afforded Rama
when making war against the demons;
he is believed to have bequeathed those villages to them as a legacy.
When a man happens to fall in with them,
and he recites to them the poetry of Rama and
pronounces the incarnations of Rama,
they will quietly listen to him;
they will even lead on the right path him who has gone astray and
give him meat and drink.
At all events, thus the matter stands according to popular belief.
- India by Al-Beruni, page 100-101
Abridged Edition of Dr. Edward C. Sachau's English Translation
Edited with Introduction and Notes by Qeyamuddin Ahmad,
Third Reprint 1995
farsakh: a persian unit for measuring distance that equals three and a half to four miles
Abu Raihan Muhammad ibn Ahmad, a Muslim of Iranian origin, commonly known as Al-Beruni, born A.D. 973 at the outskirts of Khawarizm (modern day Khiva in Uzbekistan), wrote Kitabu'l Hind in around 1030 during the reign of Sultan Mahmud. He was the first person to document Hindu beliefs regarding Setubandha, now known as Ram Setu.