Musnad Ahmad 941:72

He said: I read to Abd al-Rahman: Malik, from Musa ibn Uqbah, and [another chain] narrated to us Rawh, from Malik, from Musa ibn Uqbah, from Kurayb, the freed slave of Ibn Abbas, from Usamah ibn Zayd, that he heard him say: The Messenger of Allah (peace and blessings of Allah be upon him) departed from Arafat until, when he was at the mountain pass, he dismounted and urinated, then he performed ablution, but he did not perform the ablution thoroughly. I said to him: "The prayer?" He said: "The prayer is ahead of you." Then he mounted. When he reached Muzdalifah, he dismounted and performed ablution, and he performed the ablution thoroughly. Then the prayer was called, and he prayed Maghrib. Then every person made his camel kneel in his place. Then the prayer was called, and he prayed it [Isha], and he did not pray anything between them.