For reasons I'm not sure I can fully articulate, I would suggest if you insist on using all of those words the following arrangement:
I just hope he walks out from the probe clean.
But I don't think that idiom is necessarily the best-suited expression to go with probe. There are two reasons. First, walks away from, at least to me, is two idioms:
- to end negotiations without a deal:
Speaker John Boehner walked away from the debt talks with President Barack Obama.
- to survive something:
Canadians walked away from a car crash.
Clearly, you're hoping to use the expression with the latter meaning. But in general, this meaning applies to one-time tragic events or things that you don't have to undergo for a long time.
I take a probe as google defines it as a an investigation into a crime or other matter to refer to something that might take weeks, i.e. an inquiry. Consequently, the image gets kind of mixed -- if you are hoping that he can abandon the probe if a little unclear, then this is fine. If you are hoping that he can survive the probe, the metaphor may not be adequate due to the ambiguity in its meaning. To put it another way,
The investigator walked away from the probe.
is a truly ambiguous sentence. It's caught between whether the investigator is the one pursuing the probe who has given up on its success and whether he is the one being probed in which case he escapes without harm. My sense is that the form possibility is much higher.
As such, I would recommend saying something else:
I hope he makes it through the probe.
Here, I'm assuming that what you want to emphasize is your hope that he survives the ordeal -- not that he can abandon it.