Musnad Abu Ya'la al-Mawsili 110:14

Uthman ibn Abi Shaybah narrated to us, Hushaym narrated to us, from Ibn Abi Layla, from al-Hakam, from Miqsam, from Ibn Abbas, who said: When the Prophet, peace and blessings of Allah be upon him, arrived at Khaybar, he gave its land and its palm trees [to the people of Khaybar] to cultivate on the basis of a sharecropping agreement for half [of the produce].