I'm not the one that discovered this, the one that did was Flufffybuns (Actually, it was discovered by someone earlier than Flufffy but they deleted the video so God knows who that person was)
Original Link: https://soundcloud.com/undertale-recreated/undertale-bonus-track-sans-voice-recreation
OG clip: https://www.youtube.com/watch?v=_SP0NJWHiHw