B’Midbar Rabah 23:9:
When Eliyahu said to the worshippers of Baal, ‘Choose for yourselves one bull and make [your offering] first, for you are the majority’ (I Kings 18:25), four hundred and fifty prophets of Baal and four hundred and fifty prophets of Asherah gathered together, but they could not move the bull’s foot from the ground…
What did Eliyahu do? He said to them, ‘Choose identical bulls from the same mother, who grew up on the same pasture, and cast upon them lots, one for the Almighty and one for Baal.’ …
Eliyahu’s bull immediately was drawn after him. As for the bull that was chosen for Baal, all the prophets of Baal and the prophets of Asherah gathered together but could not move its foot, until Eliyahu said, ‘Go with them.’
The bull answered and said to him, ‘In the eyes of all the people I and my fellow emerged from one womb, [fathered] by one bull, and grew up on one pasture, and his [lot] came up in the portion of G-d, and the name of the Holy One Blessed is He is sanctified over him, but my [lot] came up in the portion of Baal, to anger my Creator!’
Eliyahu said to it, ‘O bull, O bull, do not fear! Go with them, so that they do not find fault [with me], for just as the name of the Holy One Blessed is He is sanctified over that [bull] that is with me, so is it sanctified over you.’
[The bull] said to [Eliyahu], ‘This is what you advise me? I swear I will not move from here until you give me over into their hand!’ As it says: ‘They took the bull that he gave to them’ (ibid v. 26). Who gave to them? Eliyahu.
UPDATED July 20: Also see Tanchuma Masey 8 for a similar account.