Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.27

3.2.2.27

nainamanyatra carantamabhyastamiyāt | na svapantamabhyudiyātsa yadenamanyatra carantamabhyastamiyādrātrerenaṃ tadantariyādyatsvapantamabhyudiyādahna enaṃ tadantariyānnātra prāyaścittirasti pratigupyamevaitasmāt na purāvabhṛthādapo 'bhyaveyānnainamabhivarṣedanavakLptaṃ ha tadyatpurāvabhṛthādapo 'bhyaveyādyadvainamabhivarṣedatha parihvālaṃ vācaṃ vadati na mānuṣīm prasṛtāṃ tadyatparihvālaṃ vācaṃ vadati na mānuṣīm prasṛtām

Let not the sun set on him while abiding elsewhere (than the hall); nor let the sun rise on him while asleep. For were the sun to set on him while abiding elsewhere, he (the sun) would cut him off from the night; and were the sun to rise on him while asleep, he would cut him off from the day: there is no atonement for this, hence it must by all means be avoided. Prior to the purificatory bath he should not enter water, nor should it rain upon him; for it is improper that he should enter water, or that it should rain upon him, before the purificatory bath. Moreover, he speaks his speech falteringly, and not effusively after the manner of ordinary speech. The reason why he speaks his speech falteringly and not after the manner of ordinary speech is this: