Place this clip late in a FNAF edit, after the build-up and before the payoff scare. Follow it with the FNAF jumpscare scream for the sudden turn, or end the sequence there if the next scene is a lore breakdown.
About this sound
This clip is Purple Guy's sung part from It's Been So Long, a short vocal line delivered in character over music. It feels mournful and unsettling, with the regret in the singing making the moment land heavier than a plain quote. It comes from the Five Nights at Freddy's fan song about the Purple Guy's story.