Musnad Abu Ya'la al-Mawsili 154:32

Abu Hisham al-Rifa'i narrated to us, Ibn Fudayl narrated to us, Abu Hayyan al-Taymi narrated to us, from 'Ata' ibn Abi Rabah, from Ibn 'Umar, who said: I was sitting with the Prophet, may Allah bless him and grant him peace, when a Bedouin came to him and said, "Do you have any interest in goodness? Testify that there is no god but Allah and that Muhammad is the Messenger of Allah." He [the Prophet] said, "And who will testify for you?" He said, "This acacia tree." So he called it, and it was on the bank of the valley. It came, furrowing the earth, until it stood before him. He asked it to testify, and it testified three times, then it returned to its place. The Bedouin said, "I will go to my people; if they follow me, I will bring them to you, and if not, I will return to you and be with you."