"Leave thou thy sister, when she prays"
Public DomainTennyson

The verse comes from "In Memoriam" by the 19th century poet, Alfred Lord Tennyson. Tennyson wrote the poem to commemorate his friend Arthur Hallam, who died suddenly of a brain haemorrhage. Like Tennyson, Hallam was a student at Trinity College, Cambridge. He was due to marry Tennyson's sister but died before the wedding could take place.