from the Synaxarion:
The Holy Martyrs Manuel, Sabel and Ismael, brothers by birth, were descended from an illustrious Persian lineage. Their father was a pagan, but their mother was a Christian, who baptised the children and raised them with firm faith in Christ the Saviour. Having grown into adults, the brothers entered military service. Speaking on behalf of the Persian emperor Alamundar, they were his emissaries in the concluding of a peace treaty with the emperor Julian the Apostate (361-363). Julian received them with due honour and showed them his favour. But when the brothers refused to take part in a pagan sacrificial offering, Julian became angry, and annulling the treaty, he locked up the peace emissaries of a foreign country in prison, like common criminals. At the interrogation he told them, that if they scorned the gods worshipped by him, it would be impossible to reach any peace or accord between the two sides. The holy brothers answered that they were sent as emissaries of their emperor on matters of state, and not arguments about gods. Seeing the firmness of faith of the holy brothers, the emperor gave orders to subject them to fierce tortures.
They suspended the holy martyrs, having nailed their hands and feet to wood, at their heads they thrust nails, and under their finger-nails and toe-nails they wedged sharp needles. During this time of torment the saints, as though not feeling the tortures, glorified God and prayed. Finally, they beheaded they holy martyrs. Julian ordered their bodies to be burned. But suddenly there occurred an earthquake, and the ground opened up and took the bodies of the holy martyrs into its bosom. After two days, following upon the fervent prayers of Christians, the earth returned the bodies of the holy brothers, from which issued forth a fragrance. Many pagans, having witnessed the miracle, came to believe in Christ and were baptised. Christian reverently buried the bodies of the holy Martyrs Manuel, Sabel and Ismael. This occurred in the year 362. And since that time the relics of the holy passion-bearers have been glorified with wonder-working.
Having learned about the murder of his emissaries, and that the law-transgressor Julian was marching against him with a numerous army, the Persian emperor Alamundar gathered up his army and started off towards the border of his domain. In a large battle the Persians vanquished the Greeks. Julian the Apostate was killed by the holy Great-Martyr Mercurius (Mercury, Comm. 24 November).
Thirty years later the pious emperor Theodosius the Great (+ 397) built at Constantinople a church in honour of the holy martyrs, and Sainted Germanos, Patriarch of Constantinople (Comm. 12 May), then still a priestmonk, wrote a canon in memory and in praise of the holy brothers.