Just recently, I believed that spaces between words were first invented with the Carolingian minuscule, invented by the English scholar Alcuin of York. As I just discovered, spacing wasn't first ever used with Alcuin's Carolingian minuscule. Apparently, before Alcuin, Irish monks in the early Middle Ages had (re?)invented spacing between words.
However, I then came across this academic monograph which said that one of the reasons Irish monks developed spacing is because they were copying Syriac Bible's, and these already had spacing between words (the source was Paul Saenger's Space between Words: The Origins of Silent Reading though I have no access to the relevant part of this monograph to check). I'm aware that Syriac is a dialect of Aramaic. Suddenly, this information is starting to get a bit confusing and the sources I'm looking for aren't completely clear.
So I wanted to ask: what was the first alphabet to actually use spacing between words? I'm not talking about word-separation with points and interpuncts, rather, the practice of placing an empty space to separate two words (Carolingian minuscule being an example).
I'd also be thankful to be pointed to the scholarly literature on exactly this question.