Musnad Abu Ya'la al-Mawsili 109:239

Abu Khaythama narrated to us, Rawh narrated to us, Ibn Jurayj narrated to us, he said: ‘Ata’ said: I heard Jabir saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Do not combine fresh dates (rutab) and unripe dates (busr), nor raisins and dried dates (tamr).”