It is in the 5e PHB as mentioned by others, yeah. It's honestly so ingrained in the way I think about games personally that I find it odd it ever had to be spelled out in the first place. Obviously the specific rules have to take precedence if they contradict a more general rule, or otherwise there'd be barely any design space in a game at all. It'd be like saying Action Surge doesn't actually do anything because you can only take one action per turn. Ridiculous on its face, right? Maybe there's something I don't know.

I'm not clear on this, but I think I first heard "specific beats general" in the context of explaining how MTG worked when that game was new; did D&D inherit the phrase when WOTC acquired it and made 3e, or am I just wrong?