Several Islamists have been circulating above certificate by saying that UNESCO has declared as such, but the UNESCO declared on 11.07.2016 by its website that the purported certificate is fake and the never issued such by UNESCO.
The UNESCO statement :
UNESCO denounces fake statement
We wish to refer to the recent allegations posted on the website juntakareporter, citing an alleged statement and certificate from UNESCO declaring “Islam as the most peaceful religion of the world”. Such statement was never made by the Organization and that the certificate reproduced on this website is a fake one. The website that published this information is a satirical media.
UNESCO has never had any official relationship with the entity referred to as “International Peace Foundation”, nor has it ever supported such a statement or granted any diploma of this kind.
In line with its mandate, the Organization has the responsibility to promote interreligious and intercultural dialogue on a global scale, with the unerring support of its Member States, partners and networks. In doing so, UNESCO promotes respect on equal grounds for all traditions and faiths, always striving to build bridges and strengthen ties whenever possible.
NOVEMBER 13TH, 2019
Additional mentioning: https://timesofindia.indiatimes.com/times-fact-check/news/fake-alert-no-unesco-has-not-declared-islam-as-the-worlds-most-peaceful-religion/articleshow/70071918.cms