I'm sure that the sahaba were used to remind each other of the teachings of our Prophet (), so it could certainly be that Sahabi A has witnessed the Prophet doing or saying something, while Sahabi B was not present, but heard it through Sahabi A.

If Sahabi B now was to transmit this narration to a tabi'i (and so on) what would this hadith be called, is there a specific term for this in the hadith sciences?

What if Sahabi B said the Prophet said/did ... (without quoting sahabi A) would that also be called tadlees? (If this would make the answer too long and needs a separate question, maybe one could discuss it in What exactly is tadlees? or I might ask a new question)