Manava Dharmashastra 2.221

2.221

pūrvaprāyaścittavidherayamarthavādaḥ | nimlocanenābhidrutaḥ abhinirmuktaḥ | evamabhyuditaḥ | prāyaścittaṃ pūrvoktaṃ na karoti | tadā mahatā pāpena sambadhyate, na svalpena | narakādiduḥkhopabhoganimittamadṛṣṭaṃ 'pāpa'mucyate |

If during one’s sleep the sun has set, and if during one’s sleep the sun has risen,—if he does not perform the Expiatory Rite, he becomes tainted by grievous sin.—(221)

Medhātithi’s commentary (manubhāṣya):
This is a commendatory statement pertaining to the aforesaid injunction of the expiatory rite.

He who becomes tainted by the setting of the sun,—similarly who becomes tainted by the rising of the sun;—and he does not perform the expiatory rite prescribed above,—then he becomes tainted by ‘grievous’—not minor—‘sin.’ ‘Sin’ is the name of that unseen force which leads one to suffer pain in the form of living in hell and so forth.—(221)