The Vishnu Sahasranama is found in the Mahabharatha, in the Anushasanika Parvam (chapter relating to orders or rules to the kings). Literally translated this means thousand names of Vishnu.
Bheeshma Pitamah was defeated and grievously wounded by Arjuna. Since he had the boon of icha mrtyu, he could choose the time of his death and was waiting for Uttarayana, the northward journey of the sun. Meanwhile, the war came to an end, leading to the death of all the male members in his family except for the Pandavas and the unborn child of Abhimanyu. Yudhishtra, the eldest of the Pandavas became the King of Hasthinapura and sought for guidance from Bheeshma the great. Anushasanika Parva is in the form of questions and answers between Yudhishtra and Bheeshma Pitamah and Vishnu Sahasranama is taught by Bheeshma to Yudhishtra.
Discourses:
By Brhm. Pratyagaatma Chaitanya from Arsha Vidya Gurukulam
JNANA MANDIR 