Sorry if this question seems redundant to some others, but I'm having a really hard time trying to figure this one out. I've been searching the internet on this for a while now and can't seem to get a clear answer.
So let me explain. I want to put a novel together, like a historical fiction of sorts, about the Japanese ninja. I've been reading English translations of some old ninja scrolls, namely the Bansenshukai. The Bansenshukai is considered like a "ninja manual." Anyway, for example, this book has things explained very clearly, like some of the spying tactics used, ways to predict weather, how to read people, and it even cites some prayers. If I decide to move forward with writing this novel, would it be legal for me to use and reference some of the things mentioned in this book? Should I reference and give credit to the Bansenshukai or whatever scroll I'm using for some of the activities shown in the book? As for the prayers, would it be OK for me to write them word for word within the book as long as I give proper credit, or should I just avoid it altogether?
I'm trying to make this novel interesting but as close to real history as possible. Again, it's totally fictional but I'm using real-world actions. I just don't know if something like, for example, chanting a prayer, or how to tell if it's going to rain today, is something that's necessarily copyrighted. But it's already been published in another book, so that makes me wonder if I should at least give credit.
Any insight is appreciated.