It goes without saying that Islam is a religion which pays attention to the cleanliness, decency, and the good appearance and smell of its adherents. Muslims are recommended to appear decent and clean. They also are to keep their mouth clean by using a brush or siwak (tooth stick, also known as miswak). The Prophet commanded his companions to use siwak in cleaning their teeth and continued to use it while fasting. Abu Dawud and At-Tirmidhi report an authentic hadith narrated by `Amir ibn Rabi`ah. He said: “I have seen the Messenger of Allah (peace and blessings be upon him) using a tooth-stick (siwak) while he was fasting more often than I could count.”
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: It is absolutely fine to brush one’s teeth in the morning with toothpaste while fasting so long as one takes care not to swallow the paste. It is reported in the sunnah that the Prophet (peace and blessings be upon him) was seen brushing his teeth quite a number of times during the day while he was fasting. Toothpaste is not intended for consumption. Fast is only broken when it goes directly into our system. To say that one cannot use toothpaste is nothing but rigidity. The Prophet (peace be upon him) warned us against rigidity: “Woe to those who practice rigidity; woe to those who practice rigidity; woe to those who practice rigidity.” (Reported by Muslim)
By avoiding brushing with toothpaste, we end up offending the public by the foul odours of the mouth. Remember it is far more important for us to avoid such objectionable things than being rigid on such frivolous interpretations which have no valid ground in Islam.
The eminent Muslim scholar, Sheikh Yusuf Al-Qaradawi, adds: Using a brush while one is fasting is not blameworthy, provided that no toothpaste or similar substances reach the stomach. If anything reaches the stomach, it breaks one’s fast according to the majority of Muslim jurists. If one is cautious and brushes his teeth and out of forgetfulness some traces reach his stomach, he is not sinful, as Allah forgives the mistakes of Muslims that are made unintentionally. Allah, Exalted be He, says: (And there is no sin for you in the mistakes that ye make unintentionally.) (Al-Ahzab 33: 5) And the Prophet (peace and blessings be upon him) is reported to have said: “My nation shall not be held accountable for the mistakes they do unintentionally, out of forgetfulness, and under duress.” (Reported by Ibn Majah)