Yazid bin Bilal narrates from Sayyiduna Ali (may Allah be pleased with him) that he said: When you fast, use the miswak in the morning and do not use the miswak in the evening, for there is no fasting person whose lips become dry in the evening except that they will be a light between his eyes on the Day of Resurrection.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8336