Source: Rabbi Hananel

Hello, Your Honor, the Rabbi
I am currently watching the series God and the World and I am waiting and enjoying it very much, thank you.
I know that many people don’t like being asked about sources. I would appreciate it if you would excuse me. In lesson 5, the rabbi mentions the words of our Rabbanu Hananel in the celebration of the fifth day, that a person who kills his friend is not in the heavenly realm, and it is said, “And there is one who perishes without trial.” I looked in the source and didn’t find what I was looking for.
I know that the Rabbi’s opinion is that the mention of the opinion in the Rishonim is not the main point and that they are not relying on it, but rather stating that they also believed so. I would be happy to know if there is a source for this idea in our Rabbi Hananel to strengthen it with me and with others. I am still captive to a preconceived opinion. What should I do, especially in light of what is mentioned in the Rishonim that the words of Rabbi Hananel are words of Kabbalah and were passed down in tradition, and therefore their importance is great.
Thank you very much for the good news and again sorry for the inconvenience.