Yahya bin Urwah bin al-Zubayr narrates from his father (Urwah, may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever revives barren land that did not belong to anyone before him, it is his, and the one with an unjust root has no right." He said: The man (involved in) this hadith told me that he saw two men of Banu Bayadah bringing a dispute to the Messenger of Allah (peace and blessings be upon him) over a thicket that belonged to one of them, in which the other had planted date palms. The Messenger of Allah (peace and blessings be upon him) ruled in favour of the landowner for his land, and ordered the owner of the palms to remove his palms from it. He said: I saw him striking at the roots of the palms with axes, even though they were 'umm palms. Yahya bin Adam said: Concerning al-'umm, some said: it is one that is neither short nor tall; some said: al-'umm means old; and some said: tall. The Shaykh said: It has been narrated from Muhammad bin Ishaq bin Yasar that he said: al-'umm means young.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب إحياء الموات / 11776