Sayyiduna Ibn Umar (may Allah be pleased with them both) said: We were with the Messenger of Allah (peace and blessings be upon him) on a journey when a Bedouin approached. When he came near, the Prophet (peace and blessings be upon him) said to him: "Where are you headed?" He said: To my family. He (peace and blessings be upon him) said: "Would you like something good?" He said: What is it? He (peace and blessings be upon him) said: "That you bear witness that there is no true god except Allah, alone, without partner, and that Muhammad is His servant and Messenger." He said: Who is a witness to what you say? He (peace and blessings be upon him) said: "This tree." So the Messenger of Allah (peace and blessings be upon him) called it, and it was on the bank of the valley. It came, ploughing through the earth, until it stood before him (peace and blessings be upon him). He (peace and blessings be upon him) asked it to testify three times, and it testified that the matter was just as he (peace and blessings be upon him) had said. Then it returned to the place where it grew. And the Bedouin went back to his people and said: If they follow me, I will bring them to you; otherwise I will come back to you myself and stay with you.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13525