O salutaris hostia (English O Saving Host) is the penultimate stanza of the hymn Verbum supernum prodiens, composed by St. Thomas Aquinas for the Hour of Lauds in the Office of the Feast of Corpus Christi. This stanza and the final stanza, or doxology (Uni trinoque Domino), have been selected to form a separate hymn for Benediction of the Most Blessed Sacrament. Usually, and most appropriately, it is begun either when the door of the tabernacle is opened or when the monstrance is being placed on the throne of exposition. The hymn is often chosen as a motet for solemn Mass, and may thus be used after the proper Offertory for the day has been sung or recited.

This popular melody was written by Anthony Werner (1817-1866) in the mid-19th century. The well-known melody of Tantum Ergo originated in a Stonyhurst manuscript in 1751 and was  arranged and published in London by Samuel Webbe (1740–1816) in his Motets and Antiphons, 1792.

The text is by Thomas Aquinas. Gregorio Allegri was an Italian priest, composer, and tenor in the Papal Choir. Adoremus in Aeternum was the concluding antiphon at Benediction of the Blessed Sacrament. This well-known setting was  adapted by Sir Richard Terry in the late 19th century for use at Downside Abbey in England. The verses are sung to Gregorian Psalm Tone I.

Verse 1
O salutaris Hostia
Quae caeli pandis ostium
Bella premunt hostilia
Da robur, fer auxilium

Verse 2
Uni Trinoque Domino
Sit sempterna gloria
Qui vitam sine termino
Nobis donet in patria