Atharvaveda 9.4.1

9.4.1

sāhasrás tveṣá r̥ṣabháḥ páyasvān víśvā rūpā́ṇi vakṣáṇāsu bíbhrat |
bhadráṃ dātré yájamānāya śīkṣan bārhaspatyá usríyas tántum ā́tān ||1||

The bright bull of a thousand, rich in milk, bearing all forms in his bellies, desiring to accomplish (? çikṣ) what is excellent for his giver, the sacrificer—he, the ruddy one of Brihaspati, hath stretched ⌊ā-tan⌋ the line (tántu).