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A small fraction of quasars show an unusually high nitrogen-to-carbon ratio(N/C) in their spectra. These "nitrogen-rich" (N-rich) quasars are along-standing puzzle because their interstellar medium implies stellarpopulations with abnormally high metallicities. It has recently been proposedthat N-rich quasars may result from tidal disruption events (TDEs) of stars bysupermassive black holes. The rapid enhancement of nitrogen and the depletionof carbon due to the carbon--nitrogen--oxygen cycle in supersolar mass starscould naturally produce high N/C. However, the TDE hypothesis predicts that theN/C should change with time, which has never hitherto been observed. Here wereport the discovery of the first N-rich quasar with rapid N/C variability thatcould be caused by a TDE. Two spectra separated by 1.7 years (rest-frame) showthat the N III]\lambda 1750/C III]\lambda 1909 intensity ratio decayed by~86%+/-14% (1 \sigma). Optical (rest-frame UV) light-curve and X-rayobservations are qualitatively consistent with the TDE hypothesis; though, thetime baseline falls short of a definitive proof. Putting the single-objectdiscovery into context, statistical analyses of the ~80 known N-rich quasarswith high-quality archival spectra show evidence (at a 5\sigma\ significancelevel) of a decrease in N/C on timescales of >1 year (rest-frame) and aconstant level of ionization (indicated by the C III]\lambda 1909/C IV\lambda1549 intensity ratio). If confirmed, our results demonstrate the method ofidentifying TDE candidates in quasars via abundance ratio variability, openinga new window of TDE observations at high redshift (z>2) with upcominglarge-scale time-domain spectroscopic surveys.

A Candidate Tidal Disruption Event in a Quasar at z=2.359 from Abundance Ratio Variability