Musnad Ahmad 509:16

Waki’ narrated to us, al-A’mash narrated to us, from al-Minhal ibn ‘Amr, from Ya’la ibn Murrah, from his father, who said: I was with the Prophet, may Allah bless him and grant him peace, on a journey, and he stopped at a place. He said to me: "Go to those two acacia trees and say to them: 'The Messenger of Allah, may Allah bless him and grant him peace, commands you both to come together.'" I went to them and said that to them, and one of them leaped toward the other, and they came together. The Prophet, may Allah bless him and grant him peace, came out and screened himself with them, and he relieved himself. Then, each one of them leaped back to its place.