Text:
Et erit firmamentum…
Et erit firmamentum…
The same antiphon verse can be read in the Leon Antiphoner (fol. 45v, link to the digital edition http://bvpb.mcu.es/es/catalogo_imagenes/grupo.cmd?posicion=96&path=26408... ) for the same liturgical occasion. See RANDEL, Don M., An Index to the Chant of the Mozarabic Rite, Princeton: Princeton University Press, 1973, p. 64.