SB 6.1.42

sūryo ’gniḥ khaṁ marud devaḥ
 somaḥ sandhyāhanī diśaḥ
kaṁ kuḥ svayaṁ dharma iti
 hy ete daihyasya sākṣiṇaḥ
Synonyms: 
sūryaḥ — the sun-god; agniḥ — the fire; kham — the sky; marut — the air; devaḥ — the demigods; somaḥ — the moon; sandhyā — evening; ahanī — the day and night; diśaḥ — the directions; kam — the water; kuḥ — the land; svayam — personally; dharmaḥ — Yamarāja or the Supersoul; iti — thus; hi — indeed; ete — all of these; daihyasya — of a living entity embodied in the material elements; sākṣiṇaḥ — witnesses.
Translation: 
The sun, fire, sky, air, demigods, moon, evening, day, night, directions, water, land and Supersoul Himself all witness the activities of the living entity.
Purport: 

The members of some religious sects, especially Christians, do not believe in the reactions of karma. We once had a discussion with a learned Christian professor who argued that although people are generally punished after the witnesses of their misdeeds are examined, where are the witnesses responsible for one’s suffering the reactions of past karma? To such a person the answer by the Yamadūtas is given here. A conditioned soul thinks that he is working stealthily and that no one can see his sinful activities, but we can understand from the śāstras that there are many witnesses, including the sun, fire, sky, air, moon, demigods, evening, day, night, directions, water, land and the Supersoul Himself, who sits with the individual soul within his heart. Where is the dearth of witnesses? The witnesses and the Supreme Lord both exist, and therefore so many living entities are elevated to higher planetary systems or degraded to lower planetary systems, including the hellish planets. There are no discrepancies, for everything is arranged perfectly by the management of the Supreme God (svābhāvikī jñāna-bala-kriyā ca). The witnesses mentioned in this verse are also mentioned in other Vedic literatures:

āditya-candrāv anilo ’nalaś ca
 dyaur bhūmir āpo hṛdayaṁ yamaś ca
ahaś ca rātriś ca ubhe ca sandhye
 dharmo ’pi jānāti narasya vṛttam