I wouldn't say there's any one good resource. Most people preach intermittent fasting, which I've found is okay for maintenance and health but it's not nearly as beneficial nor will it lose you as much weight as fasting for days on end. But here's some material I went over to educate myself and convinced me that it's perfectly safe:
Fasting vs. Eating Less: What's the Difference? (Science of Fasting)
https://www.youtube.com/watch?v=APZCfmgzoS0
Dr. Jason Fung - 'Therapeutic Fasting - Solving the Two-Compartment Problem'
https://www.youtube.com/watch?v=tIuj-oMN-Fk
Beginners Guide to Prolonged Fasting | 24-72 Hour Fasting Instructions
https://www.youtube.com/watch?v=S5W1XBf8d-I
^^ Not exactly a fan of Thomas DeLauer but there's some good information there.
If you aren't faint of heart, check out some videos on the "Snake Diet" channel on YouTube. Cole is kind of a lunatic, constantly swears, and holds nothing back. He does this to be motivational. He's wrong about a few things(he thinks fasting cures everything and also thinks vaccines are bad), but when it comes to fasting properly he's pretty spot on. I just took from him what I thought made sense and left the rest behind. The best idea I got from him was the "snake juice", which is really just an electrolyte mixture you can make at home. It really makes all the difference.
Overall, I wish there was someone who could preach this stuff without the Cole's level of insanity, but there you have it.