The full Ring poem is:
Three Rings for the Elven Kings under the sky
Seven for the Dwarf Lords in their Halls of Stone
Nine for the Mortal Men doomed to die
One for the Dark Lord on his dark throne
In the Land of Mordor where shadows lie
One Ring to rule them all
One Ring to find them
One Ring to bring them all and in the darkness bind them
In the Land of Mordor where shadows lie.
In Black Speech, the fictional language of Mordor, it is:
Ash nazg durbatulûk, ash nazg gimbatul, ash nazg thrakatulûk agh burzum-ishi krimpatul
The part that is written on the One Ring is:
"One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them."
https://en.wikipedia.org/wiki/One_Ring
[Added reference link - McG]