Sayyiduna Amir bin Rabi'ah al-Adawi (may Allah be pleased with him) narrates: I cannot count how often I saw the Prophet (peace and blessings be upon him) using the miswak (tooth-stick), and he (peace and blessings be upon him) would use the miswak while fasting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8325