Musnad Abu Ya'la al-Mawsili 42:25

Zuhayr narrated to us, Yahya bin Sa’id narrated to us, Sa’d bin Ishaq narrated to us, Zaynab bint Ka’b narrated to me, from Abu Sa’id, that the Messenger of Allah (may Allah bless him and grant him peace) declared sacred what is between the two lava fields (labbatan) of Medina, that its trees should not be cut or beaten.