What is the ruling on one who performs istinja' but does not perform wudu' until a long time has passed?

It is not a condition for the validity of ablution (wudu') that it be immediately preceded by istinja' (washing after defecation or urination). Istinja' is performed after relieving oneself to cleanse the area from external impurities. Once istinja' is done and the area is purified, there is no need to repeat istinja' again when performing ablution, no matter how long the time between them. In fact, performing istinja' due to flatulence is an innovation (bid'ah). The assumption that ablution is not valid unless preceded by istinja', even if there is no cause for it, is a mistake and an extremism. Istinja' is not part of ablution, and its place is after one has finished relieving oneself.