I didn't see anything online about a resignation anywhere so share a link if you have anything about a resignation. In Whit's press conference, he just said that Fuente didn't want to coach the last two games if his future status was not guaranteed by Whit. Whit said that he was considering keeping Fuente but there was no guarantee. I pasted a couple relevant excerpts below.

A little bit on timing so you know how we got to this point. Justin and I meet every Wednesday. We have for a long time. We met last week. It was at a point in time that I could not tell him with certainty that he would continue to be the coach here. I said I was strongly considering it. And then at that point, when he realized he would likely not be the next coach, he wanted to move on, and I respect that opinion.

Did you want him [Fuente] to finish the season?

Yeah, certainly. I want to say this two ways: I certainly would have liked for that to happen, but I also understand Justin’s point that, ‘hey, if I’m not the guy and you don’t believe in me, then we need to do this.’ I don’t want to paint Justin in a poor corner. I don’t think he quit on anybody. I think his meeting with the team today was great. And I don’t know how I would handle it if the roles were reversed. But yes, he had that option.