Manava Dharmashastra 5.143

5.143

kṣutvā anicchato vāyupreryamāṇasya yo nāsikācchidrādupajāyate śabdaḥ sa kṣavathustaṃ kṛtvā | prayato'pi san | etadadhyeṣyamāṇapadenaiva sambadhyate | prayato'pyadhyeṣyamāṇa ācamyādhīyīta, adhyayanavidhyaṅgatayā''camanaṃ kuryādityarthaḥ | snānādibhyastvanantaraṃ sakṛdeva | yatpunaruktam"suptvā kṣutvā ca bhuktvā ca pītvā''po vai munistathā | ācāntaḥ punarācāmenniṣṭhovyoktvā'nṛtaṃ vacaḥ ||" iti | evamabhisambandho'tra kartavyaḥ, 'ācānto bhuktvā punarācāmet' | yatra punardvirācāmediti paṭhyate tatrānantaryaiṇaikakriyāvṛttiḥ |

Medhātithi’s commentary (manubhāṣya):
‘After having sneezed,’—after having done sneezing, which is the name given to the sound that emanates involuntarily from the nostrils of a man moved by internal wind.

‘Even though he may be quite pure.’—This is to be construed only with the phrase‘when going to read the Veda’; the meaning being that even though he be quite pure, he should, when going to read the Veda, read it after having sipped water; i.e., the water sipping-should be done as part of the procedure laid down in connection with Vedic study; while after sleep &c., the water-sipping shall be done once only.

As for the following declaration—‘Having slept, having sneezed, having eaten, having drunk water, the wise man shall sip water and then again sip water; as also after having spat and told lies’,—this has to be construed to mean that ‘having sipped water, he should eat and then sip water again.’ In a case however where it is clearly stated that ‘one should sip water twice, the act has to be repeated consecutively.’ (143)