Musannaf Ibn Abi Shayba 36:333

'Abd al-Rahim ibn Sulayman narrated to us, from Hajjaj ibn Artah, from Makhul, from Zayd ibn Jariya, from Habib ibn Maslama, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to grant an extra share (nafal) from the spoils of war. In its beginning (the initial phase of the expedition), it was a fourth, and in its return (the latter phase), it was a third.