Musnad Ahmad 175:29

Ibrahim ibn Abi al-Abbas narrated to us, Abu Uways narrated to us, he said: Al-Zuhri said: Abd al-Rahman ibn Abd Allah al-Ansari informed me, that Ka'b ibn Malik used to narrate that the Messenger of Allah, peace and blessings of Allah be upon him, said: "The soul of the believer is but a bird that feeds upon the trees of Paradise, until Allah, the Exalted, returns it to his body on the day He resurrects him."