Almighty and everliving God, who didst strengthen thine apostle Thomas with sure and certain faith in thy Son’s resurrection: Grant us so perfectly and without doubt to believe in Jesus Christ, our Lord and our God, that our faith may never be found wanting in thy sight; through him who liveth and reigneth with thee and the Holy Spirit, one God, now and for ever.
I’m seeing this in various locations, but I thought the feast was in July? According to the Catholic Almanac:
[i]Thomas (Didymus): Notable for his initial incredulity regarding the Resurrection and his subsequent forthright confession of the divinity of Christ risen from the dead; according to legend, preached the Gospel in places from the Caspian Sea to the Persian Gulf and eventaully reached India where he was martyred near Madras; Thomas Christians trace their origin to him; in art, is depicted knelling before the risen Christ, or with a carpenter’s rule and square; feast, [b]July 3 (Roman Rite), Oct. 6 (Byzantine Rite)[/b]. [/i]