Paithinasidharmasutra 1.1: Smṛticandrikā · Smṛtiratnākara · Ācārādarśa +3

1.1

antarudakam ācānto 'ntar eva śudhyati | bahirudakam ācānto bahir eva śudhyati | tasmād bahir ekam antar ekaṃ ca kṛtvā pādam ācamane sarvatra śuddho bhavati

One who sips water [for purification] with both feet in the water becomes pure only in the water; one who sips outside the water becomes pure only outside. Therefore, placing one foot outside and one foot inside when sipping water, he becomes pure everywhere.

One who sips water standing in the water is pure only within it; one who sips outside is pure only outside. Therefore, with one foot outside and one inside, one is pure everywhere when sipping.