Duke University canceled plans Thursday to begin a weekly Muslim call to prayer from the campus chapel this week, an initiative that had set off debate on social media. A school spokesman and a Duke Muslim leader said that a serious and credible security threat played a role in the decision. The university had announced that Muslim students would chant the ‘adhan,’ the call to a weekly prayer service, from the Duke University Chapel bell tower each Friday. The sound of the call to prayer in Muslim communities is a standard part of ritual life on Muslims’ main prayer day. Theologically, it reminds Muslims “to worship God and serves as a reminder to serve our brothers and sisters in humanity,” Imam Adeel Zeb, Muslim chaplain at Duke, said in a news release. But reaction to the story off campus was swift. Some celebrated the decision.