{He that believeth on me} (ho pisteu(936e) eis eme).
Nominative absolute as is not uncommon. {The scripture} (h(880a)graph(885c)). No precise passage can be quoted, though similar idea
in several ( Isa 55:1  58:11  Zec 13:1  14:8  Eze 47:1  Joe
3:18 ). Chrysostom confines it to  Isa 28:16  by punctuation
(only the nominative absolute as the Scripture). {Out of his
belly shall flow rivers of living water} (potamoi ek t(8873) koilias
autou reusousin hudatos z(936e)tos). Some ancient Western writers
connect pinet(935c) of verse  37  with ho pisteu(936e) in verse  38 .
By this arrangement autou (his) with koilias is made to refer
to Christ, not to the believer. Burney argues that koilia is a
mistranslation of the Aramaic (fountain, not belly) and that the
reference is to  Eze 47:1 . C.C. Torrey refers to  Zec 14:8 . But
the Eastern writers refer autou (his) to the believer who not
only quenches in Christ his own thirst, but becomes a source of
new streams for others ( Joh 4:14 ). It is a difficult question
and Westcott finally changed his view and held autou to refer
to Christ. Reusousin is future active indicative of 
e(935c), old
verb, to flow, here only in the N.T.