Sa'id bin Isa (may Allah have mercy on him) narrates from his grandmother that she heard Sayyidah Umm Habibah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), say: "The fasting person should not chew gum ('ilk)."
His grandmother is Umm al-Rabi', and the hadith is mawquf (stopping at the Companion).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8306