Jaiminīya Upaniṣad Brāhmaṇa 1.40.2

1.40.2

vāg eva sāma
vācā hi sāma gāyati
vāg evoktham
vācā hy ukthaṃ śaṃsati
vāg eva yajuḥ
vācā hi yajur anuvartate /

Speech is the sāman, for with speech one sings the sāman. Speech is the uktha, for with speech one recites the uktha. Speech is the yajus, for with speech one follows along with the yajus.