Musnad Ahmad 483:4

Hammad ibn Khalid—who is al-Khayyat—narrated to us, from Mu'awiyah—meaning Ibn Salih—from al-'Ala' ibn al-Harith, from Makhul, from Zayd ibn Jariyah, from Habib ibn Maslamah: "That the Messenger of Allah (may Allah bless him and grant him peace) granted a fourth (of the spoils) as an extra reward after the fifth (the khums) during his initial advance, and he granted a third (of the spoils) as an extra reward after the fifth (the khums) during his return."