Shatapatha Brahmana 7.5.1.33

7.5.1.33

agne yukṣvā hi ye tava | yukṣvā hi devahūtamāniti yuktavatībhyāmidamevaitadyonau reto yunakti tasmādyonau reto yuktaṃ na niṣpadyate

[Vâg. S. XIII, 36-37; Rik S. VI, 16, 43 VIII, 75,1] 'O Agni, harness those good steeds of thine: they draw equal to thy mettle!--Like a chariot-fighter, harness thou the steeds, the best callers of the gods, O Agni! take thy seat as the old Hotri!' with two (verses) containing the (verb) 'yug' (to harness, fasten),--he thus settles that seed injected into the womb, whence the seed settled in the womb does not escape.