Is the hadith about the tree moving in response to the Prophet Muhammad's command—when a non-Muslim man asked him for a sign—authentic?

Al-Darimi mentioned that Ibn Umar narrated that the Prophet, peace and blessings be upon him, called a tree, and it came to him and bore witness to his prophethood, then returned to its place. An Arab Bedouin who was with him then embraced Islam. Similarly, Ibn Abbas narrated that the Prophet, peace and blessings be upon him, called a cluster of dates from a palm tree, and it descended to him then returned, whereupon an Arab Bedouin embraced Islam after witnessing that.