Dietrich Bonhoeffer, The cost of discipleship I.4 ("Discipleship and the cross") (2nd rev. and unabridged edition, trans. R. H. Fuller and Irmgard Booth (New York: The Macmillan Company, 1959), 79).
The original German, though, is much more prosaic:
"Jeder Ruf Christi fährt in den Tod."
Every call of Christ leads to death.
See Discipleship I.4 ("Discipleship and the cross"), trans. Barbara Green and Reinhard Krauss, Dietrich Bonhoeffer works, ed. Wayne Whitson Floyd, Jr., vol. 4, ed. Geffrey B. Kelly and John D. Godsey (Minneapolis: Fortress Press, 2001), 87 and 87n11.