In the Holy Qur'an

Say (as for) the death from which you flee, that will surely overtake you, then you shall be sent back to the Knower of the unseen and the seen (62:8)

In the Traditions

The Holy Prophet said, “Remember the destroyer of pleasures.”
When asked what that was, he replied, “Death. Wherever one of Allah’s servants remembers this when he is wealthy, this world is constricted for him. Wherever he remembers it in hardship, it is expanded for him.”

Imam Ali said, “Wash the dead and your heart will be moved, for surely an empty body is a profound lesson.”