shake in one's boots

/SH EY1 K IH0 N W AH0 N EH0 S B UW0 T S/
verb
  1. 1

    To be very frightened, scared, or nervous.

    โ€œThe thought of climbing that high had him quaking in his boots.โ€

Source: https://en.wiktionary.org/wiki/quake%20in%20one's%20boots, https://en.wiktionary.org/wiki/shake%20in%20one's%20boots