Musannaf Ibn Abi Shayba 36:334

Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Abd al-Rahman ibn al-Harith ibn ‘Ayyash ibn Abi Rabi’ah al-Zuraqi, from Sulayman ibn Musa, from Makhul al-Shami, from Abu Salam al-A’raj, from Abu Umamah al-Bahili, from ‘Ubadah ibn al-Samit, that the Messenger of Allah (may Allah bless him and grant him peace) used to grant as *nafal* (extra spoils) one-fourth at the beginning [of the expedition] and one-third upon the return.