Ziyad bin Hudayr narrates: I have not seen anyone more persistent in using the miswak while fasting than Sayyiduna Umar (may Allah be pleased with him). I think he said: with a stick. Abu Ubayd said: meaning a dry stick.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8329