Daily Hadith Day 14: Fasting 14th Ramadan 1430 (4th September 2009)

Narrated Abu Huraira (Radi-Allahu 'anhum):

The Prophet (Sallallahu 'Alaihi Wa Sallam) said, "If somebody eats or
drinks forgetfully then he should complete his fast, for what he has eaten
or drunk, has been given to him by Allah." Narrated 'Amir bin Rabi'a, "I
saw the Prophet (Sallallahu 'Alaihi Wa Sallam) cleaning his teeth with
Siwak while he was fasting so many times as I can't count." And narrated
Abu Huraira, "The Prophet (Sallallahu 'Alaihi Wa Sallam) said, 'But for my
fear that it would be hard for my followers, I would have ordered them to
clean their teeth with Siwak on every performance of ablution." The same is
narrated by Jabir and Zaid bin Khalid from the Prophet (Sallallahu 'Alaihi
Wa Sallam) who did not differentiate between a fasting and a nonfasting
person in this respect (using Siwak).

Aisha  (Radi-Allahu 'anha) said, "The Prophet (Sallallahu 'Alaihi Wa
Sallam) said, "It (i.e. Siwak) is a purification for the mouth and it is a
way of seeking Allah's pleasures." Ata' and Qatada said, "There is no harm
in swallowing the resultant saliva."

Bukhari Vol. 3 : No. 154

Daily Hadith Day 14: Fasting 14th Ramadan 1430 (4th September 2009)