Shatapatha Brahmana 11.7.2.7

11.7.2.7

tadāhuḥ adhvaryo yaddīkṣitasya nānavabhṛtho'vakalpate kvainamavabhṛthamavaneṣyasīti sa yaddhṛdayaśūlena caranti sa haivaitasyāvabhṛthaḥ

As to this they say, 'Seeing that the want of the purificatory bath in the case of the initiated is improper, Adhvaryu, when didst thou take him down to the purificatory bath?' Well, when they perform with the heart-spit, that is his purificatory bath.