I am playing a cleric. I would like to take the Ritual Caster feat at level 4 to access some wizard spells for utility.
Can my cleric spend the material cost to add rituals shared by both classes (like Detect Magic, Detect Poison, Identify, Gentle Repose, etc.) to the ritual book? Or do I need to find a wizard based written source?
Best Answer
You need to find a written source
As per the Ritual Caster feat's description (PHB, p. 169; emphasis mine):
The way I understand that is you can add rituals to your rituals book, you simply need to copy it from a written source and pay the costs and spent the necessary time.
So, to be very precise, as long as the spell you want to copy is from the spell list you have chosen when taking this feat and has the ritual tag and is not higher level than half your own level (rounded up) and you have a written source for it, then you can include it in your rituals book.
Eg.: You have taken Ritual Caster (Wizard) as a cleric. You find a scroll of detect magic. As a cleric you have access to that spell, can cast it as a ritual but to do so you need to prepare it after a long rest, taking one of your preparation slot for the day. Since it is also a spell in the wizard's spell list, you could add it to your ritual book and from then on you wouldn't need to prepare Detect Magic to be able to cast it as a ritual (and as a ritual only), as long as you have your rituals book in hand.