"Not Lost but Gone Before" (ca. 1850). Burton E. Stevenson, Home Book of Quotations, and the Oxford Dictionary of Quotations trace "Not lost, but gone before" and similar expressions to Seneca, St. Cyprian, and Matthew Henry.
Albert Einstein, Harry Woolf (1980). “Some strangeness in the proportion: a centennial symposium to celebrate the achievements of Albert Einstein”, Addison Wesley Publishing Company