Musannaf Ibn Abi Shayba 5:708

Hatim ibn Isma'il narrated to us, from Jahdam ibn 'Abd Allah, from Muhammad ibn Ibrahim, from Muhammad ibn Zayd, from Shahr ibn Hawshab, from Abu Sa'id, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade the purchasing of charity items (sadaqat) until they are taken possession of.