The following antiphon is found in some medieval breviaries, today being the traditional feast of St Thomas the Apostle.
O Thoma Didyme! qui Christum meruisti cernere; te precibus rogamus altisonis, succurre nobis miseris; ne damnemur cum impiis, in adventu Iudicis.
O Thomas the Twin, who didst merit to see Christ; we beseech thee with earnest prayers, help us miserable sinners; lest we be condemned with the wicked when the Judge comes.
Guéranger's discussion of the feast of St Thomas, including this antiphon is found here. Sources for the other Great Antiphons may be found here.
