Musannaf Ibn Abi Shayba 13:2144

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Hisham ibn ‘Urwah narrated to us, from his father, that the Prophet (peace and blessings of Allah be upon him) bought a camel from a Bedouin for a wasq of dates. He sent me to Khawlah bint Hakim, and she fulfilled it for him. And he said: "The best of you are those who fulfill [their obligations] in a good manner."