Which 20th century rabbi said "G-d normally doesn't stop the ill-intentioned"?

Question

I recall hearing the following story:

There was a non-observant Israeli Jew who kept having visions of his deceased father telling him he should do more religiously. Finally he was about to turn on the radio on Yom Kippur when he had a vision of his father telling him to shape up or else. The fellow went to Rabbi X, who asked if he had done anything especially meritorious; the fellow thought, then mentioned that in his youth, he and his father had been in a Nazi Ghetto and risked a great deal to give someone a proper Jewish burial. Rabbi X explained that generally if someone has decided to do something wrong, G-d doesn't interfere; only if the person is particularly meritorious.

If you've heard this story, can you remind me please who Rabbi X was? It would have been someone living in the second half of the 20th Century.

Answer 1

I'm not sure to which Rav you're referring, but the Gemara in Masechet Shabbat 104A (Hebrew, English) states that "one who comes to defile himself is given an opening (i.e. he is permitted, but not actively helped) and one who comes to cleanse himself [...] is helped":

בא ליטמא פותחין לו בא ליטהר מסייעים אותו

Answer 2

I contacted someone who asked the rabbi from whom I'd heard it. It was the Chazon Ish.

(Which makes sense; he wrote a lot about free will. Fascinatingly, it was his opinion that when we pray for there to be less evil in the world, we are praying that G-d tamper with wicked people's free will. R' Moshe Feinstein disagreed.)