Musnad Ahmad 25:532

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, he said: Al-Harith ibn Fudayl al-Ansari narrated to me, from Mahmud ibn Labid al-Ansari, from Ibn Abbas, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "The martyrs are at Bariq—a river at the gate of Paradise—in a green dome. Their provision comes out to them from Paradise morning and evening."