What is the ruling on going against Istikhara, and is one sinful for doing so?

Istikhara is recommended when embarking on a matter where the right course of action is unclear. After performing Istikhara, the supplicant should proceed with what their heart feels at ease with. If they go against this and do something their heart was not at ease with, there is no sin upon them. Whatever they do after a legitimate Istikhara is good. What they perceive as evil after doing something their heart was not at ease with might actually be a good that Allah averted from them. Istikhara is a supplication whose answer may not manifest in this world; rather, its reward may be stored for the Hereafter, or it may avert a calamity.