CHĀNDOGYA UPANISHAD · 1.12.4

ते ह यथैवेदं बहिष्पवमानेन स्तोष्यमाणाः संरब्धाः सर्पन्तीत्य् एवम् आससृपुः ।
ते ह समुपविश्य हिञ् चक्रुः ॥

te ha yathaivedaṃ bahiṣpavamānena stoṣyamāṇāḥ saṃrabdhāḥ sarpantīty evam āsasṛpuḥ ।
te ha samupaviśya hiñ cakruḥ ॥

The dogs came on, holding together, each dog keeping the tail of the preceding dog in his mouth, as the priests do when they are going to sing praises with the Vahishpavamâna hymn. After they had settled down, they began to say Hiṅ.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)