Manava Dharmashastra 2.9

2.9

yo nāstikatayā vaidikāni niṣphalāni karmāṇīti vyāmuhya na tadanuṣṭhāne pravarteta tasya pravṛttyarthaṃ suhṛdbhūtvā dṛṣṭaphalapradarśanaṃ karoti | tiṣṭhatu tāvadanyatphalam | śrutau smṛtiṣu ca yaduditamuktaṃ dharmākhyaṃ karma tadanutiṣṭhannihāsmim̐lloke yāvajjīvati tāvatkīrtiṃ praśasyatāṃ pūjyatāṃ saubhāgyaṃ labhate | nyāyye pathi sthito mahāpuṇyo'yamiti sarveṇa pūjyate, priyaśca sarvasya bhavati | pretya dehāntare | yasmādanyaduttamaṃ nāsti tatsukhaṃ prāpnoti | prāyeṇa svargakāmasyādhikāraḥ | niratiśayā ca prītiḥ svargasta ucyate hyanuttamamiti | tasmānnāstikasyāpi dṛṣṭaphalārthino'traiva pravṛttiḥ prayuktetyevamparametat |

For the man performing the duty laid down by the revealed word and the recollections obtains fame here, and after death, unsurpassed happiness.—(9)

Medhātithi’s commentary (manubhāṣya):
There might be some one who, being an unbeliever, might form the misconception that the acts laid down in the Veda are fruitless, and omit to do them; hence with a view to induce such a man to undertake the performance of those acts, the Author, placing himself in the position of a friend, proceeds to indicate the. perceptible results that follow from the acts in question, to say nothing of other kinds of results.

The man who performs the act, known as ‘duty,’ ‘Dharma,’—which is ‘laid down by the Revealed Word and the Recollections—obtains ‘here,’ in this wold, as long as he lives, ‘fame,’ praise, honour, regard; that is, all men respect him and love him as one ‘who is firm in the rightful path and highly virtuous.’

‘After death,’—in another body—he obtains that ‘happiness’ superior to which there is no other happiness. As a matter of fact, almost all the acts are prescribed in the Veda as to be done by one who desires Heaven; and ‘Heaven’ stands for ‘unsurpassed happiness’; hence it is that the author speaks of ‘unsurpassed happiness.’

For these reasons, it is only right that the unbeliever also, who seeks for nothing but visible results, should undertake the performance of the acts in question. This is the purport of the text.—(9)