Amir Ibn Rabia narrates: “I saw Hz. Muhammad (PBUH) using a miswak while fasting more times than I can count.” (Bukhari, Sawm: 27; Abu Dawud, Savm: 26; Tirmidhi, Sawm: 29)

Ibn Umar Radiyallahu Anhuma reports:

The fasting person uses miswak at the beginning and end of the day. (Bukhari, Sawm 25)

As it is understood from the Hadiths, using miswak while fasting is a deed that belongs to Ahl-i Sunnah of our Prophet (PBUH). However we see that our Religious sect Imams, who have authority on the subject of Sunnah, do Ijtihad for the details of some subjects by considering all riwayahs (narration).

According to Imam Abu Yusuf, it is makrooh for the fasting person, to use a miswak or a toothbrush which is dampened with water. It is not makrooh when a fasting person uses a miswak or a toothbrush dampened with water according to Imam Azam and Imam Muhammad. However using a toothbrush with toothpaste is definitely makrooh when fasting. It is necessary to avoid using it. But it does not invalidate the fast.