In the context of Christianity, the obvious examples are the apostles, who claimed to have been firsthand eyewitnesses of the resurrection of Jesus (with the exception of the apostle Paul, who didn't witness the resurrection but still claimed to have had a "Damascus Road" encounter). They maintained their testimonies despite opposition, persecution and even death as martyrs.
Are there similar historical examples outside of Christianity?
To be clear, a Muslim Jihadist would not count as an example unless he explicitly claimed to have been a firsthand eyewitness of a miracle and maintained his testimony in spite of persecution until martyrdom.
The Wikipedia article on martyrs was obviously the first thing I checked before I posted this question, but I was not able to identify a specific case of non-Christian martyrdom in which the reason for the persecution was that the individual claimed to have been a firsthand witness of a miraculous event, leading to beliefs that endangered established orthodoxies, the established order or anything of that sort.
I also attempted to find examples by googling "martyr eyewitness miracle" and similar queries, but I only managed to find Christian examples, such as the Martyrdom of Polycarp, which allegedly involved miraculous events (see the first paragraph in the Wikipedia article).