Paris attacks: 'I will not give you the gift of hating you'
18 November 2015 Last updated at 17:32 GMT
Antoine Leiris lost his wife Helene in the Bataclan theatre in Paris.
His Facebook tribute to his wife and challenge to her killers has since been shared thousands of times.
Mr Leiris read out the letter to BBC News in Paris.
Video by: Alice Doyard and Maarten Lernout
Edited by Mohamed Madi