Old Irish version of the Sunday Letter (Carta Dominica), a letter allegedly written by Christ insisting on strict Sunday observance. In the manuscripts it is commonly found together with another Old Irish text, Cáin Domnaig.
The so-called third or ‘modern’ recension of In tenga bithnua, preserved mainly in copies of the 18th and 19th centuries, though the oldest copy may date from the 15th century.