Musannaf Ibn Abi Shayba 30:163

Husayn ibn Ali narrated to us, from Za'idah, from Maysarah al-Ashja'i, from Ikrimah, from Ibn Abbas, who said: I asked Ka'b, "What is the Lote Tree of the Utmost Boundary (Sidrat al-Muntaha)?" He said, "A lote tree at which the knowledge of the angels ends, and at it they find the command of God; knowledge does not go beyond it." And I asked him about the Garden of Abode (Jannat al-Ma'wa), and he said, "A garden in which there are green birds, in which the souls of the martyrs ascend."