Musnad Ahmad 1007:102

'Affan narrated to us, Aban narrated to us, Yahya ibn Abi Kathir narrated to us, 'Abdullah ibn Abi Qatadah narrated to me, from his father: That the Prophet, peace and blessings of Allah be upon him, forbade the mixing of unripe dates (*busr*) and dried dates (*tamr*), and the mixing of raisins and dried dates, and the mixing of fresh dates (*zahw*) and ripe dates (*rutab*). He said: And Abu Salamah ibn 'Abd al-Rahman narrated to me, from Abu Qatadah, from the Prophet, peace and blessings of Allah be upon him, the like of it.