Where does Augustine say that the rapture of the saved soul will "flow over" into the glorified body? In The Weight of Glory, C. S. Lewis writes:


  What would it be to taste at the fountainhead that stream of which even these lower reaches prove so intoxicating?  Yet that, I believe, is what lies before us.  The whole man is to drink joy from the fountain of joy.  As St. Augustine said, the rapture of the saved soul will "flow over" into the glorified body.  In light of our present specialised and depraved appetites, we cannot imagine this torrens voluptatis, and I warn everyone most seriously not to try.


I haven't been able to find where Augustine actually said this.  Where in Augustine's writings is the original quote and its context?
Arend Smilde finds the answer to this question in Augustine's letter to Dioscorus (CXVIII), 3.14:


  Now, perfect health of body shall be the consummation of the immortality of the whole man. For God has endowed the soul with a nature so powerful, that from that consummate fulness of joy which is promised to the saints in the end of time, some portion overflows also upon the lower part of our nature, the body,—not the blessedness which is proper to the part which enjoys and understands, but the plenitude of health, that is, the vigour of incorruption.


The reference to torrens voluptatis is apparently distinct, using phrasing from the Vulgate and Augustine's exposition of Psalm 35:9 (or, 36:8):


  “And of the torrent of Thy Pleasure shalt Thou give them to drink.” [et torrente voluptatis tuae potabis eos] A torrent we call water coming with a flood. There will be a flood of God’s Mercy to overflow and inebriate those who now put their trust under the shadow of His wings. What is that Pleasure? As it were a torrent inebriating the thirsty. Let him then who thirsts now, lay up hope: whoso thirsts now, let him have hope; when inebriated, he shall have possession: before he have possession, let him thirst in hope. “Blessed are they which do hunger and thirst after righteousness, for they shall be filled.”