You can find the downloadable sheet here: musescore.com/user/27331185/s...
O filii et filiæ ("O sons and daughters") is a Easter christian hymn.
The text was written by the french friar minor Jean Tisserand, a well-known preacher (... - Lyon, 1497)
The hymn became very popular in France, from where it spread to other countries.
The triple alleluia between the verses is sung by a voice and repeated by the choir, while a solo voice sings the odd-numbered verses with their final alleluia. The even-numbered verses are sung by the choir.