The earliest known portion of this quote I could find was on the epitaph of Edward of Woodstock, the Black Prince of Wales, son of King Edward III.
He passed at the age of 45 on June 8th, 1376. The phrase composes the first two lines of the epitaph upon his tomb in Canterbury Cathedral, Kent, England.
His epitaph read as such:
Such as thou art, sometime was I.
Such as I am, such shalt thou be.
I thought little on th'our of Death
So long as I enjoyed breath.
But now a wretched captive am I,
Deep in the ground, lo here I lie.
My beauty great, is all quite gone,
My flesh is wasted to the bone
Hope this helps!