1 Thessalonians 4:13-18 is where we are told to comfort one another with and in hope about death. And there are a few other comforting sayings you could use too, which are not in the Bible though.
Life is but a stopping place,
a pause in what's to be,
A resting place along the road
to sweet eternity.
We all have different journeys,
different paths along the way,
We all are meant to learn some things,
but, never meant to stay...
Our destination is a place
far greater than we know.
For some the journey's quicker
for some the journey's slow.
And when the journey finally ends,
we claim a great reward
And find an everlasting peace,
Together with our Lord.
You can sign your card, "May God speed healing to all your broken hearts."