Heh, I've had this album for a year, and first heard that song yesterday. The part comes in the middle of the song; I recognised it instantly. It was such a delight, I'm considering listening to this album again once I'm more familiar with Pentangle just to see what else I can pick out.
"Pentangling" by The Pentangle, a well-regarded British folk/jazz/blues outfit. I believe the vocal samples in this song are from them as well. There are other samples from them on other songs, perhaps. I know the end of Busy Signal is from the end of another Pentangle song entitled "Let No Man Steal Your Thyme".