Arvo Pärt - Sarah Was Ninety Years Old (Part 2 of 3) 

Arvo Pärt - Composition: Sarah Was Ninety Years Old. This is 25 minutes long so you need to hear Part 1 of 3, Part 2 of 3, and Part 3 of 3 to hear everything. Singing for Part 2 starts at 1:55. Composed in 1977 and updated in 1991. This is the Hilliard Ensemble performance.
NOTE - There is an error in the video that shows an image of an "old" Arvo Part. This is not Arvo Pärt, it is Archimandrite Sophrony, the dedicatee of Pärt's Silouans Song.