This epitaph is taken from a line the poem title A Farewell, by historian and author Charles Kingsley, written in the mid 1800's.

A Farewell

My fairest child, I have no song to give you;
No lark could pipe to skies so dull and gray;
Yet, ere we part, one lesson I can leave you
For every day.

Be good, sweet maid, and let who will be clever;
Do noble things, not dream them, all day long:
And so make life, death, and that vast forever
One grand, sweet song.

Kingsley also later published an alternate version of this poem:

A Farewell To C. E. G.

My fairest child, I have no song to give you;
No lark could pipe in skies so dull and gray;
Yet, if you will, one quiet hint I'll leave you,
For every day.
I'll tell you how to sing a clearer carol
Than lark who hails the dawn or breezy down;
To earn yourself a purer poet's laurel
Than Shakespeare's crown.

Be good, sweet maid, and let who can be clever;
Do lovely things, not dream them, all day long;
And so make Life, and Death, and that For Ever,
One grand sweet song.