Was it ever revealed (in an interview, script draft, etc.) what Daniel whispered to Eli in the church after the baptism in There Will Be Blood? It certainly looked like Eli was not pleased with hearing whatever it was. I think I've seen two script drafts with no mention, but maybe there were others.
I have no interest in saying that there is no answer. But I want to point out that this has been discussed a lot online and no one has any idea. It's not in PT Anderson's script for the film, and there is no audio in the film at all in regards to something being whispered. It only occurs visually. Also, there is no mention of anything like this in the book!
What we might be able to conclude is that it was an acting choice, but Anderson had no interest it playing the decision out to the audience, and leaving it in as a sort of "environmental" decision (idk if that makes sense. I just mean that it visually adds to the intensity, but doesn't have a direct impact on the plot).
"It's not in the script, nor the soundtrack, nor the subtitles. It's left to your imagination or else it was just a bit of ad-libbing on the actors' part. My interpretation was Daniel was telling Eli off after allowing Eli to humiliate him."