It's often attributed to Biblical verses, such as Ecclesiastes 8:15 ("Then I commended joy, because a man has nothing better under the sun than to eat and drink and be joyful, and this will accompany him in his labor all the days of his life that God gives him under the sun.") or Ecclesiastes 9:7 ("Go, eat your food with joy, and drink your wine with a merry heart, for God has already approved what you do.").
However, these verses don't explicitly state "tomorrow we die" but rather focus on enjoying life while you can.
The phrase is likely a reflection of a carpe diem (seize the day) philosophy and has been used in various contexts throughout history.