Answer:
Perhaps you might be thinking of the passage from Proverbs:
Like an infected tooth or an unsteady foot is (dependence on) a faithless man in time of trouble. Prov 25:19 NAB.
Or perhaps Habakkuk:
Decay invades my bones, my legs tremble beneath me. Hab 3:16 NAB
Or perhaps Sirach:
Why are dust and ashes proud? Even during life man's body decays. Sirach 10:9 NAB