Śvetadvīpa-varṇana and Śāstra-pravartana (Śānti Parva 322)
उपतिष्ठति तिष्ठन्तं गच्छन्तमनुगच्छति । करोति कुर्वत: कर्म च्छायेवानुविधीयते
upatiṣṭhati tiṣṭhantaṃ gacchantam anugacchati | karoti kurvataḥ karma chāyevānuvidhīyate ||
Bhishma said: Karma follows a person like a shadow. When one stands, it stands close by; when one walks, it walks behind; when one goes, it goes along. Whatever a doer does, that very deed—together with its moral consequence—keeps pace with him and never lets him go.
भीष्म उवाच
A person cannot escape the consequences of their actions: karma adheres to the doer as closely as a shadow, accompanying them in every state—standing, moving, or acting—until it bears fruit.
In the Shanti Parva’s instruction on dharma, Bhishma delivers a moral maxim to Yudhiṣṭhira: he illustrates, through the image of a shadow, how deeds and their results inevitably follow the agent.