Malik (may Allah have mercy on him) relates from Abdullah bin Abi Bakr (may Allah have mercy on him) that a letter came from Umar bin Abd al-Aziz (may Allah have mercy on him) to my father while he was at Mina, (saying) that zakah is not to be taken from horses or from honey.
Imam al-Shafi'i (may Allah have mercy on him) says: Sa'd bin Abi Dhubab (may Allah be pleased with him) relates what indicates that the Messenger of Allah (peace and blessings be upon him) did not command him to collect zakah from honey, and that it was something he himself saw fit, and his people gave it to him voluntarily. Al-Za'farani says that Imam al-Shafi'i (may Allah have mercy on him) said: The hadith that "there is a tithe on honey" is weak, and the one that "the tithe is not to be taken from it" is (also) weak, except from Umar bin Abd al-Aziz. My choice is that it is not taken from it, because the Sunnahs and reports are established regarding what it is taken from, and they are not established regarding it, so it is as though it is exempted.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7466