It is narrated from Sayyiduna Khabbab (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When you fast, use the tooth-stick (miswak) in the morning and do not use it in the evening, for there is no fasting person whose lips become dry in the evening except that this will be a light between his eyes on the Day of Resurrection."
The narrator said: Sayyiduna Ali (may Allah be pleased with him) did not narrate it as marfu' (attributed to the Prophet).
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3681