[AJC]

Silmarillion- pg 365 paper back Version
Chapter - The three rings of power and the third age;
Specifically the 7 year siege in the valley of Gorgoroth at the beginning of the movie when Sauron comes forth and kills Anarion son of Elendial, Gil-galad and Elendil and Isildur uses Narsil the sword to cut the ring from Saurons hand.

Unfinished tales
Chapter- The Disaster of the Gladden Fields; when Isildur is ambushed and slain by orc arrows as he tries to escape the battle swimming in the river while wearing the one ring. The ring slips off his hand and he is spotted and shot with arrows by orcs. Page 271 Hard Back Version - this is a detailed account of the battle.