Death! to the happy thou art terrible;
But how the wretched love to think of thee,
Oh thou true comforter, the friend of all
Who have no friend beside!

Robert Southey (1774–1843) English Romantic poet, Poet Laureate

Joan of Arc, Book 1, l. 318ff (1840 ed.)
    (Source)

These lines are from the final version (1840) Southey published, the work having gone through substantial rewriting multiple times, as his reputation, talent, and politics evolved. The lines are not in the first (1796) edition as published. In the 1798 edition, we find:

Bitter art thou to him that lives in rest,
O Death! and grievous in the hour of joy
The thought of thy cold dwelling; but thou comest
Most welcome to the wretched; a best friend
To him that wanteth one; a comforter.
For the grave is peace.